Malesian Euphorbiaceae Descriptions

103. TRIGONOSTEMON (Euphorbiaceae)

P.C. van Welzen & R.-Y. Yu

Yu, R.-Y. & van Welzen, P.C. 2018. A taxonomic revision of Trigonostemon (Euphorbiaceae) in Malesia. Blumea 40: 179–229.

Yu, R.-Y., Slik, F.J.W. & van Welzen, P.C. 2019. Molecular phylogeny of Trigonostemon and its relatives (Euphorbiaceae). Taxon 68: 918–936.

Yu, R.-Y., Agoo, E.M.G., Callado, J.R. & van Welzen, P.C. 2020. Taxonomic notes on Trigonostemon (Euphorbiaceae) in the Philippines. Blumea 65: 12–24.

Yu, R.-Y. & van Welzen, P.C. 2020. A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia. Blumea 65: 25–52.

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Genus description

Key to the sections

Sections

Key to the species

Regional Keys

    Key to the species of the Malay Peninsula

    Key to the species of Sumatra

    Key to the species of Java

    Key to the species Borneo

    Key to the species of the Philippines

    Key to the species of The Lesser Sunda Islands

    Key to the species of New Guinea

Species descriptions

Doubtful Species

Excluded Names

Trigonostemon Blume

    Trigonostemon Blume, Bijdr. (1825) 600 (‘Trigostemon’); Fl. Javae (1828) Preface 8 (name corrected in note), nom. cons.; Baill., Étude Euphorb. (1858) 340, plate 11, fig. 12; Müll.Arg. Linnaea 34 (1865) 212; in A.DC., Prodr. 15, 2 (1866) 1105; Benth. in Benth. & Hook.f., Gen. Pl. 3 (1880) 298; Hook.f., Fl. Brit. India 5 (1887) 395; Pax in Engl. & Prantl, Nat. Pflanzenfam. 3, 5 (1890) 84; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 85; Ridl., Fl. Malay Penins. 3 (1924) 263; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 451; Gagnep. in Lecomte, Fl. Indo-Chine 5 (1925) 309; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169; Jabl., Brittonia 15 (1963) 151; Backer & Bakh.f., Fl. Java 1 (1963) 495; Airy Shaw, Kew Bull. 26 (1972) 344; Whitmore, Tree Fl. Malaya 2 (1973) 134; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 201; Kew Bull. 32 (1978) 415; Kew Bull. 35 (1980) 690; Kew Bull., Addit. Ser. 8 (1980) 205; Kew Bull. 36 (1981) 352; Kew Bull. 37 (1982) 36; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 46; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 108; R.I.Milne, Kew Bull. 49 (1994) 445; Kew Bull. 50 (1995) 25; Kew Bull. 50 (1995) 51; H.S.Kiu, Fl. Reipubl. Popul. Sin. 44(2) (1996) 162; Philcox in Dassan., Fl. Ceyl. 11 (1997) 110; Radcl.-Sm., Gen. Euphorbiacearum (2001) 307; Chantar.,Thai Forest Bull. (Bot.) 33 (2005) 21; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 573; P.T.Li & M.G.Gilbert. in C.Y.Wu, P.H.Raven & D.Y.Hong, Fl. China 11 (2008) 272; G.L.Webster in Kubitzki, Fam. & Gen. Vasc. Pl. 11 (2014) 171; R.Y.Yu & Welzen, Blumea 62 (2018) 182. — Trigonostemon Blume Sect. Eutrigonostemon Müll.Arg., Linnaea 34 (1865) 214, nom. inval.; in A.DC., Prodr. 15, 2 (1866) 1108; Benth., J. Linn. Soc., Bot. 17 (1878) 224; in Benth. & Hook.f., Gen. Pl. 3 (1880) 298; Hook.f., Fl. Brit. India 5 (1887) 396; Pax in Engl. & Prantl, Nat. Pflanzenfam. 3, 5 (1890) 84; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 88; in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169. — Trigonostemon Blume Sect. Trigonostemon: Jabl., Brittonia 15 (1963) 158. — Type: Trigonostemon serratus Blume.

    Enchidium Jack, Malayan Misc. 2 (1822) 89, nom. rej.; Baill., Étude Euphorb. (1858) 652; Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1256 (‘Enchidion’); Merr., J. Arnold Arbor. 33 (1952) 224. — Type: Enchidium verticillatum Jack (= Trigonostemon verticillatus (Jack) Pax).

    Silvaea Hook. & Arn., Bot. Beechey Voy. (1837) 211 non Phil., Fl. Atacam. 21 (1860) 21, nec Meisn. in A.DC., Prodr. 15, 1 (1864) 84; Baill., Étude Euphorb. (1858) 341. — Trigonostemon Blume Sect. Silvaea (Hook. & Arn.) Müll.Arg., Linnaea 34 (1865) 214; in A.DC., Prodr. 15, 2 (1866) 1110. — Type: Silvaea semperflorens (Roxb.) Hook. & Arn. (= Trigonostemon semperflorens (Roxb.) Müll.Arg.).

    Athroisma Griff., Not. Pl. Asiat. 4 (1854) 477, nom. inval., non DC. in Guillem. Arch. Bot. (Paris) 2 (1833) 516. — Syntypes: Athroisma dentatum Griff. (=? Trigonostemon longifolius Wall. ex Müll.Arg.; see Hook.f., Fl. Brit. India 5, 1887: 396; Pax & Hoffmann in Engler, Pflanzenr. IV.147.iii, 1911: 88), Athroisma serratum Griff. (=? Trigonostemon heteranthus Wight; see Hook.f., Fl. Brit. India 5, 1887: 396; Pax & Hoffmann in Engler, Pflanzenr. IV.147.iii, 1911: 91; =? Trigonostemon longifolius Wall. ex Müll.Arg.; see Airy Shaw, Kew Bull. 26, 1972: 347).

    Telogyne Baill., Étude Euphorb. (1858) 327, plate 11, fig. 13. — Trigonostemon Blume Sect. Telogyne (Baill.) Müll.Arg., Linnaea 34 (1865) 214; in A.DC., Prodr. 15, 2 (1866) 1107; Benth., J. Linn. Soc., Bot. 17 (1878) 225; in Benth. & Hook.f., Gen. Pl. 3 (1880) 298; Hook.f., Fl. Brit. India 5 (1887) 398; Pax in Engl. & Prantl, Nat. Pflanzenfam. 3, 5 (1890) 84; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169; Jabl., Brittonia 15 (1963) 152. — Type: Telogyne indica Baill. (= Trigonostemon verticillatus (Jack) Pax).

    Tylosepalum Kurz ex Teijsm. & Binn., Natuurk. Tijdschr. Ned.-Indië 27 (1864) 50. — Codiaeum A.Juss. Sect. Tylosepalum (Kurz ex Teijsm. & Binn.) Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1117. — Trigonostemon Blume Sect. Tylosepalum (Kurz ex Teijsm. & Binn.) Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169; Jabl., Brittonia 15 (1963) 163. — Type: Tylosepalum aurantiacum Kurz ex Teijsm. & Binn. (= Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.).

    Trigonostemon Blume Sect. Pycnanthera Benth., J. Linn. Soc., Bot. 17 (1878) 244; in Benth. & Hook.f., Pl. Gen. 3 (1880) 299; Hook.f., Fl. Brit. India 5 (1887) 398; Pax in Engl. & Prantl, Nat. Pflanzenfam. 3, 5 (1890) 84; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 92; in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169. — Lectotype (designated by Yu & Welzen, 2018): Trigonostemon diplopetalus Thwaites.

    Nepenthandra S.Moore, J. Bot. 43 (1905) 149. — Type: Nepenthandra lanceolata S.Moore (= Trigonostemon lanceolatus (S.Moore) Pax).

    Actephilopsis Ridl., Bull. Misc. Inform. Kew (1923) 360. — Type: Actephilopsis malayana Ridl. (= Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.).

    Trigonostemon Blume Sect. Dichotomae Merr., Univ. Calif. Publ. Bot. 10 (1924) 425; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169. — Type: Trigonostemon petelotii Merr. (= Trigonostemon laevigatus Müll.Arg.).

    Prosartema Gagnep., Bull. Soc. Bot. France 71 (1924) 875; in Lecomte, Fl. Indo-Chine 5 (1925) 304. — Type: Prosartema stellaris Gagnep. (= Trigonostemon stellaris (Gagnep.) Airy Shaw).

    Poilaniella Gagnep., Bull. Soc. Bot. France 72 (1925) 467; in Lecomte, Fl. Indo-Chine 5 (1925) 307. — Type: Poilaniella fragilis Gagnep. (= Trigonostemon fragilis (Gagnep.) Airy Shaw).

    Neotrigonostemon Pax & K.Hoffm., Notizbl. Bot. Gart. Berlin-Dahlem 10 (1928) 385; in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169. — Type: Neotrigonostemon diversifolius Pax & K.Hoffm. (= Trigonostemon viridissimus (Kurz) Airy Shaw).

    Kurziodendron N.P.Balakr., Bull. Bot. Surv. India 8 (1966) 68. — Type: Kurziodendron viridissimum (Kurz) N.P.Balakr. (= Trigonostemon viridissimus (Kurz) Airy Shaw).

Shrubs to trees, monoecious; branches terete, often with leaf scars, rarely with adventitious roots (T. detritiferus, T. wetriifolius Airy Shaw & Ng and T. sandakanensis Jabl.); branches often hollow; buds densely hairy. Indumentum of simple hairs (T. balgooyi and T. reidioides also stellately bundled hairs), dense on young parts. Bark often containing sticky, translucent to orange, pinkish or reddish sap. Stipules 2, small, caducous. Leaves simple, alternate, sometimes clustered near branch tips; petiole often flat or grooved above and rounded below; blade variable in shape and size, occasionally slightly asymmetric, often with 1 pair (2 pairs in T. verticillatus and T. viridissimus) of glands at base above, margin entire or laxly serrate to crenate, teeth often small, glandular (nipple-like) to falcate, both sides greenish, glabrous to hairy, often paler (except in T. oblongifolius) and more hairy on lower side; venation pinnate or triplinerved, often more or less elevated on both sides, more so below, secondary nerves often curved and connected along margin, tertiary veins sometimes scalariform, higher order veins reticulate. Inflorescences unisexual or bisexual, axillary or terminal, sometimes cauline, often thyrsoid or paniculate, sometimes reduced and cymose or racemose (especially pistillate ones), staminate flowers often clustered into short cymes, pistillate flowers often single on each node; bracts of various shapes, sometimes leaf-like. Staminate flowers less than 1 cm diam; pedicel often slender; sepals 5, imbricate when young, connate at base, outer surface often hairy, sometimes with a gland (faint to showy) near apex, inner surface often glabrous; petals 5, often contorted in buds, variously coloured, smooth on both sides or sometimes rough and papillose inside; disc annular or 5 glands, fleshy to membranous, sometimes revoluted at apex; stamens 3 or 5, filaments united into an erect androphore, latter sometimes 3- or 5-cleft at top, anthers ellipsoid, either on free part of filaments or sessile at top of androphore, dorsifixed, 2-thecate, opening extrorse via longitudinal slits, sometimes divaricate at apex, connectives sometimes with numerous dark reddish droplets (or expanded cells) with secretion; pistillode absent. Pistillate flowers of same size or larger than staminate flowers; pedicel often thickened towards apex and accrescent in fruit; perianth as staminate flowers when flowering but sepals sometimes accrescent and petals early caducous; disc often same as staminate flowers, annular or 5 glands, often thin membranous; ovary globose, narrowed evenly towards apex into a style, 3-locular, each locule with a single ovule, outer wall glabrous to hairy; style short, often indiscernible; stigmas 3, linear, often thickened at base and bifid at top. Fruits capsules, subglobose, dehiscing septicidally and partly apically loculicidally into 3 bifid cocci; pedicel often elongating and thickened; sepals and stigmas often persistent; wall woody, exocarp often (partly) splitting off; columella persistent, T-shaped. Seeds depressed globose, smooth and marbled, ecarunculate.

    Distribution — Circa 60 species, ranging from India to China, throughout SE Asia mainland and Malesia to NE Australia and the W Pacific; 38 species in Malesia.

Key to the Sections

Sections

Only the synomym names of the sections are given (literature references under genus nomenclature), per species the section is indicated.

Trigonostemon Blume section Pycnanthera

Trigonostemon Blume section Pycnanthera Benth., J. Linn. Soc., Bot. 17 (1878) 225; R.Y.Yu et al., Taxon 68 (2019) 931. — Lectotype (designated by Yu et al. 2019): Trigonostemon diplopetalus Thwaites.

Trigonostemon Blume section Spinipollen R.Y.Yu & Welzen

    Trigonostemon Blume sect. Spinipollen R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 929. — Type: Trigonostemon longifolius Wall. ex Baill.

Shrubs or small trees. Stipules subulate to falcate, often pubescent. Leaves: petiole up to 3.5 cm long, often less than 1/7 the length of the blade, hairy; blade oblanceolate, oblong to elliptic, 4–46 by 1–15 cm, glabrous or hairy. Inflorescences uni- or bisexual, axillary or terminal, paniculate or thyrsoid, flowers arranged in racemes or clustered in very short cymes or glomerules along the main rachis. Staminate flowers: pedicel slender, pubescent, base articulate; sepals elliptic, margin entire or undulate, apex acute to rounded, glabrous or pubescent outside, glabrous inside; petals often spathulate, pink, red, dark purple or rarely white, base slightly claw-like, outer surface glabrous, inner surface glabrous or very rough (T. sandakanensis), sometimes with 2 gland lobes (T. longifolius); disc annular; stamens 3 or 5, connate in a column, anthers divaricate, connective often apically forming an appendage with expanded cells of secretion; pollen grains with “croton pattern” ornamentation, subunits reduced to spines. Pistillate flowers: pedicel longer and broader than in staminate ones; sepals very slightly or not accrescent when fruiting; petals and disc as in staminate flowers; ovary slightly to densely pubescent, sometimes warty (T. longifolius); style short, stigmas bifid into 2 arms. Fruits glabrous, warty or hairy; exocarp often partly detaching. 

Trigonostemon Blume section Trigonostemon

    Trigonostemon Blume sect. Trigonostemon: Yu et al., Taxon 68 (2019) 927. — Type: as the genus

    comprises the synonymous genera: Silvaea Hook. & Arn., Telogyne Baill., Nepenthandra S.Moore

Trigonostemon Blume section Tylosepalum (Kurz ex Teijsm. & Binn.) Pax & K.Hoffm.

    Trigonostemon Blume sect. Tylosepalum (Kurz ex Teijsm. & Binn.) Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam. ed. 2, 19c (1931) 169. — Tylosepalum Kurz ex Teijsm. & Binn., Natuurk. Tijdschr. Ned.-Indië 27 (1864) 50. — Codiaeum Rumph. ex A.Juss. sect. Tylosepalum (Kurz ex Teijsm. & Binn.) Müll.Arg. in DC., Prodr. 15, 2 (1866) 1117. — Type: Tylosepalum aurantiacum Kurz ex Teijsm. & Binn. [= Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.]

    comprises the synonymous genera: Trigonostemon Blume sect. Dichotomae Merr., Prosartema Gagnep., Neotrigonostemon Pax & K.Hoffm., Kurziodendron N.P.Balakr.

Key to the Species

Regional Keys

Key to the species of the Malay Peninsula

Key to the species of Sumatra

Key to the species of Java

Key to the species Borneo

Key to the species of the Philippines

Key to the species of The Lesser Sunda Islands

Key to the species of New Guinea

1. Trigonostemon apetalogyne Airy Shaw (sect. Tylosepalum)

    Trigonostemon apetalogyne Airy Shaw, Kew Bull. 33 (1979) 534; Kew Bull., Addit. Ser. 8 (1980) 206; R.Y.Yu & Welzen, Blumea 62 (2018) 185, map 1; R.Y.Yu et al., Taxon 68 (2019) 931. — Type: Kostermans & Soegeng 340 (holo K; iso BO, L), [Indonesia,] W Papua, limestone hills E of Sukarnapura (= Hollandia = Djajapura), Polima I.

Small trees, at least 2.5 m tall, stem at least 4 cm diam; flowering branches c. 3 mm diam. Outer bark c. 0.15 mm thick, smooth, dark brown to grey, appressed pubescent on young parts; inner bark c. 2 mm thick, blackish; wood reddish brown. Stipules subulate to falcate, 0.8–1 mm long, base pubescent, apex slightly bent. Leaves: petiole terete but grooved above, 2.5–5 cm long, slightly pubescent to glabrescent, slightly thickened at both base and top; blade oblanceolate, 11–20 by 3.5–7 cm, chartaceous to coriaceous, base narrow-rounded, with 2 adaxial glands, margin distantly serrate, apex acuminate, both sides glabrous (very sparsely pubescent when young); venation penninerved, slightly pubescent on lower side when young, midrib flat above and elevated beneath, secondary nerves 9–12 pairs, small veins reticulate, often obscure. Inflorescences: unisexual; staminate flowers cauliflorous; pistillate inflorescences subterminal, up to 14 cm long, paniculate (one side branch), few-flowered at the apex of the branches; bracts lanceolate, 0.8–2 by 0.4–0.9 mm, apex acuminate, pubescent outside. Staminate flowers c. 5 mm diam; pedicel 3–5 mm long, glabrescent; sepals ovate to orbicular, 1–1.2 by 0.6–0.7 mm, glabrescent outside; petals elliptic to obovate, 2–2.5 by 1.2–1.8 mm, entire, dark yellow, glabrous; disc glandular; stamens 3, androphore 0.3–0.5 mm long, filaments 0.1–0.2 mm long, anthers ellipsoid, c. 0.2 mm long. Pistillate flowers withered (post-anthesis), c. 2.5 mm diam; pedicel c. 7 mm long and 0.8 mm diam (top) when flowering, slightly thickened towards apex, in fruit accrescent to c. 1.5 cm long and 1.3 mm diam (top), glabrescent; sepals elliptic, 1.5–2 by 0.5–1 mm, glabrescent; petals not seen; disc as staminate flowers; ovary c. 1 mm diam, glabrous; style indiscernible; stigmas c. 0.6 mm long, apically flattened and slightly bifid. Fruits and seeds unknown.

    Distribution — New Guinea (endemic).

  l = T. apetalogyne; « = T. hartleyi

    Habitat & Ecology — On limestone hills. Altitude: c. 100 m. Flowering and fruiting: August.

   Notes — 1. The species is only known from the type collection. The specific epithet indicates that the pistillate flowers lack petals, but this is very unlikely, because the petals are generally early cauducous in Trigonostemon and the specimen only has old flowers.

    2. Trigonostemon apetalogyne differs from T. hartleyi only by having 3 instead of 5 stamens.

    3. This species is also similar to T. villosus var. borneensis in leaf shape and cauliflorous staminate flowers, but we still keep it separate because of its dark yellow flowers (as recorded on the type collection; vs dark purplish in T. villosus var. borneensis) and branched pistillate inflorescences (vs not branched in T. villosus var. borneensis).

2. Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl.  (sect. Tylosepalum)

    Trigonostemon aurantiacus (Kurz ex Teijsm. & Binn.) Boerl., Handl. Fl. Ned. Ind. 3, 1 (1900) 284; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 93; in Engl. & Harms, Pflanzenfam. ed. 2, 19c (1931) 170; Jabl., Brittonia 15 (1963) 164, in obs.; Airy Shaw, Kew Bull. 23 (1969) 126; Kew Bull. 26 (1972) 345, fig. 11; Whitmore, Tree Fl. Malaya 2 (1973) 136; Airy Shaw, Hooker´s Icon. Pl. 38 (1974) tab. 3721; Kew Bull. 36 (1981) 352; Chantar. in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 576; R.Y.Yu & Welzen, Blumea 62 (2018) 187, fig. 1, map 2; R.Y.Yu et al., Taxon 68 (2019) 930; R.Y.Yu & Welzen, Blumea 65 (2020) 28, map 2. — Tylosepalum aurantiacum Kurz ex Teijsm. & Binn., Natuurk. Tijdschr. Ned.-Indië 27 (1864) 50. — Codiaeum aurantiacum (Kurz ex Teijsm. & Binn.) Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1118. — Lectotype (designated by Yu & Welzen 2018): Teijsmann s.n. (L, barcode L.2260196), Indonesia, Java, cultivated in Bogor Botanical Garden (Originally from Bangka?).

   Actephila aurantiaca Ridl., Bull. Misc. Inform. Kew (1923) 360; Fl. Malay Penins. 3 (1924) 197. — Type: Ridley s.n., Feb. 1917 (holo K, barcode K000959323), Malaya, Kelantan, Chaning Woods.

    Actephilopsis malayana Ridl., Bull. Misc. Inform. Kew (1923) 361; Fl. Malay Penins. 3 (1924) 252; M.R.Hend., J. Malay Branch Roy. Asiat. Soc. 17 (1939) 68. — Trigonostemon malayanus (Ridl.) Airy Shaw, Kew Bull. 20 (1966) 413. — Syntypes: Curtis 674 (K), Malaya, Penang, Ayer Hitam; Haniff 1611 (?), Malaya, Perak, Gunung Kerbau; Ridley 2300 (K), Malaya, Pahang, Kwala Tembeling.

Shrubs or small trees, 1.5–3(–6) m tall, stem up to 10 cm diam; flowering branches up to 2 mm thick, smooth, brownish. Bark c. 2 mm diam; sap red and sticky; wood pale brown. Stipules subulate, c. 1.5 mm long, hirsute. Leaves: petiole 0.5–3 cm long (depending on leaf size), slightly wrinkled and grooved above, more or less pubescent; blade elliptic to oblong, 8–30 by 2.5–12 cm, chartaceous to coriaceous, base acute, with 2 glands adaxially, occasionally developing into stipellae, margin distantly serrate, teeth falcate or subulate, apex acuminate, young blade reddish, mature ones dark green above, light green beneath, glabrous or scattered pubescent on lower side; venation penninerved, midrib slightly raised above, distinctly elevated beneath, nerves 8–13 pairs, straight, branched and connected near margin, small veins reticulate, often obscure. Inflorescences: staminate ones cauline, few short and condensed thyrses, often bracteolate and with 1 flower per node; pistillate ones terminal or axillary, often racemose or paniculate, sometimes mixed with a few staminate flowers; bracteate under each branch and flower, the main rachis (and sometime secondary rachises) often subtended by large, leaf-like bracts, shortly (up to 5 mm) petiolate, blade elliptic or ovate, up to 7 by 3.5 cm, base often cordate, apex acuminate. Staminate flowers c. 6 mm diam; pedicel very slender, up to 1 cm long, c. 0.1 mm diam, pinkish, glabrous; sepals unequal, oblong, 1.2–1.5 by 0.5–1 mm, imbricate, yellowish or reddish, connate at base, apex rounded, more or less pubescent outside, with an often showy gland in the middle outside; petals oblong, c. 4 by 1.3 mm, orange, with a reddish honey mark at base, visible on both sides, inside often paler and outside sometimes with whitish margin, few parallel veins often visible, apex acute, glabrous on both sides; disc glands more or less trapezoid, thick and fleshy, c. 0.2 by 0.5 mm, c. 0.2 mm thick, apex flat; stamens 3, androphore erect, c. 0.5 mm long, trifid at top, anthers free, divaricate, each theca c. 0.6 by 0.2 mm. Pistillate flowers c. 5.5 mm diam, pedicel thickening towards apex, up to c. 7 mm long, apically c. 0.7 mm diam when flowering, up to c. 2 cm long and apically c. 1 mm diam when fruiting, glabrous; sepals as in staminate flowers, persistent in fruits; petals obovate, c. 3.5 by 2 mm, orange outside and paler inside, base cuneate or somewhat claw-like, with a reddish (dark reddish pigment granules in epidermis cells visible) honey mark, apex often rounded; disc lobes broad, almost rectangular, truncate at apex, c. 0.3 by 0.7 mm, thin, membranous; ovary c. 1.1 mm diam, glabrous, light yellowish; styles short, c. 0.2 mm long, stigmas 3, light yellowish, slightly thickened, apically split and somewhat horseshoe-shaped. Fruits c. 1.2 cm diam, greenish to reddish, glabrous; sepals not accrescent; wall c. 1 mm thick; columella  c. 5.5 mm long. Seeds c. 5.5 mm diam, dark orange when dry, hilum somewhat heart-shaped or rhombic, c. 1.5 mm diam.

    Distribution — Thailand, Malay Peninsula, Sumatra, Java, Bali.

   Habitat & Ecology — Lowland evergreen (often dipterocarp) forests, growing in understorey on limestone, along streams or on hill slopes. Altitude: 0–600 m. Flowering and fruiting: all year round.

    Notes — 1. A species variable in shape and size of the leaves. It shows similarities with T. wildeorum, from which it can easily be differentiated by its racemose or paniculate pistillate inflorescences (vs pistillate flowers always inserted in leaf axils and the pistillate sepals always strongly accrescent in T. wildeorum).

    2. One specimen (P.E. Schmutz 524, Lesser Sunda Islands, Flores) with elliptic and dark brownish to greyish leaves and a short (c. 1.5 cm) staminate peduncle, seems to be an intermediate form between T. aurantiacus and T. hartleyi (endemic to New Guinea), and even the location of the collection is between W Malesia and New Guinea. Since no other specimens are known and T. hartleyi is a poorly understood species, this specimen cannot be accurately identified and the Lesser Sunda Islands is here not included in the distribution of T. aurantiacus.

3. Trigonostemon balgooyi R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon balgooyi R.Y.Yu & Welzen, Blumea 62 (2018) 188, fig. 2, map 3; R.Y.Yu et al., Taxon 68 (2019) 927. — Type: M.M.J. van Balgooy 7102 (holo L; iso K, KEP, SAN), Malaysia, Johor, Endau Rompin, Kuala Jasin, 2° 32' N, 103° 22' E.

Shrubs or small trees, 2–3 m tall, dbh 1.5–3 cm; flowering branches 3–4 mm diam. Indumentum consisting of 2 layers of hairs (except on sepals and upper surface of leaves and bracts, these glabrous or with only 1 layer of hairs), upper layer hispid, with simple long and rigid golden hairs, lower layer of stellately bundled hairs consisting of 3–5 tiny, appressed, whitish hairs originating from one papillose point. Outer bark c. 0.1 mm thick, dark brownish to greyish, hairy, often slightly fissured; inner bark 0.1–0.2 mm thick, whitish to reddish to brownish, often with sap (solidified when dry); wood creamy, reddish brown. Stipules subulate, c. 0.5 mm long, caducous. Leaves: petiole terete, 1.5–6 cm long, 1–1.5 mm diam, hairy; blade oblong to oblanceolate, 12–23 by 1.5–6 cm, chartaceous, base cuneate to acute, with 2 nipple-like glands adaxially, margin distantly serrate, teeth small, falcate, apex acuminate to caudate, upper surface medium green, slightly bullate, papillose hispid (no stellate hairs), lower surface pale green, papillose hispid and with stellately bundled hairs on venation; venation penninerved, midrib slightly elevated above and distinctly elevated beneath, nerves 9–11 pairs, curved and bow-shaped, narrowed and connected along margin, veins reticulate, often obscure above. Inflorescences: staminate ones pyramidal paniculate or racemose, sometime cauliflorous, rachis at least up to 9 cm long, c. 1 mm diam (lower part), hispid and with stellately bundled hairs; bracts lanceolate, up to 7.5 by 1.3 mm, sparsely papillose hispid above, hispid and with stellately bundled hairs beneath; pistillate ones often single-flowered, peduncles 4–6 cm long, c. 0.6 mm diam (evenly wide throughout), sparsely hispid; bracts in lower part often 1.3–1.8 by 0.4–0.5 cm, hispid and with sparse stellately bundled hairs; bracts subtending the pistillate flower cordate, 1.5–2.1 by 0.6–1.2 cm, palmately veined, sparsely hispid above and hispid and with sparse stellately bundled hairs (often along veins) beneath. Staminate flowers c. 7 mm diam; pedicel indiscernible; sepals elliptic, 1–1.5 by c. 1 mm, pale green, sparsely papillose hispid outside, glabrous inside; petals elliptic, c. 3.3 by 2.5 mm, red to maroon, both sides glabrous, sometimes with a few pustules; disc lobes glandular, 0.25–0.3 by 0.3–0.6 mm, deep purple, apex rounded, slightly recurved; stamens 5, androphore c. 0.7 mm long, 5-cleft at apex; anthers ellipsoid, each theca 0.5–0.6 mm long, connectives apically with dark purplish droplets (or expanded cells) with secretion. Pistillate flowers c. 1.2 mm diam; pedicel less than 5 mm long; sepals triangular, c. 6.5 by 4.5 mm, apex acuminate, hispid outside, sparsely hispid and with sparse stellately bundled hairs (often along veins) inside; petals orbicular, 6–7 by 5–6.8 mm, maroon; disc not seen; ovary c. 1.2 mm diam, sparsely hairy; style c. 0.2 mm long, stigmas deeply divided, free parts c. 1.5 mm long. Fruits: sepals (remnants) persistent, 1.3–1.5 by 0.55–1 mm, with sparse stellately bundled hairs outside, glabrous inside; columella 5.5–7 mm long; cocci white, with a few hairs when young and nearly glabrous when mature; wall c. 0.65 mm thick, exocarp not detaching. Seeds c. 6 mm diam, brown when dry.

    Distribution — Malay Peninsula (endemic).

  l = T. balgooyi; n =  T. beccarii; « = T. calcicolus; ▲ = T. diffusus; ▼ = T. dipteranthus; u = T. filiformis

    Habitat & Ecology — Lowland primary (dipterocarp) rainforest on clay soil on hillside or riverside. Flowering: March to April, July; fruiting: July.

    Note — The only species in Malesia that has stellately bundled hairs, which makes it quite unique (T. reidioides in Thailand and Indochina also has stellately bundled hairs). The cordate bracts of the pistillate flowers are also distinct. The pistillate disc was not seen because it was covered by petals in the only flower present on the available material.

4. Trigonostemon beccarii Ridl. (sect. Trigonostemon)

    Trigonostemon beccarii Ridl., Bull. Misc. Inform. Kew (1925) 89; Jabl., Brittonia 15 (1963) 165; Airy Shaw, Kew Bull. 36 (1981) 353; R.Y.Yu & Welzen, Blumea 62 (2018) 189, fig. 3, map 3; R.Y.Yu et al., Taxon 68 (2019) 927. — Type: Beccari PS 965 (K, L), Sumatra, Padang, Sungei Buluh.

    Trigonostemon longisepalus Ridl., Bull. Misc. Inform. Kew (1925) 89; Jabl., Brittonia 15 (1963) 165. — Type: C.J. Brooks 8274 (holo K), Sumatra, Lubok Tandai.

Shrubs; flowering branches 1.6–4.5 mm diam, sometimes hollow. Outer bark 0.1–0.2 mm thick, brownish to greyish, smooth; inner bark 0.1–0.2 mm thick, dark reddish brown; wood white to pale reddish brown. Stipules falcate, 0.5–0.7 mm long, glabrous. Leaves: petiole 0.25–1.5 cm long, grooved above, glabrous to glabrescent; blade oblong to oblanceolate, 8–28 by 1.5–7 cm, base cuneate, adaxially 2 glands present but caducous, margin slightly distantly serrate, apex acuminate, upper side dark greenish, lower side pale green, both sides glabrous; midrib slightly raised on both sides, nerves 10–14 pairs, very slightly raised beneath, often obscure, small nerves reticulate, obscure. Inflorescences bisexual, axillary to subterminal, often 1 pistillate flower on the top and few short scorpioid cymes (glomerules) of staminate flowers along the rachis below; rachis 3–12 cm long, 0.5–0.7 mm diam, glabrous; bracts elliptic to lanceolate, 0.7–1.5 by 0.3–0.6 mm, glabrous to pubescent, apex acuminate to rounded. Staminate flowers c. 4.5 mm diam; pedicel c. 3.5 mm long, c. 0.3 mm diam, glabrescent; sepals elliptic, c. 1 by 0.7 mm, apex rounded, slightly ciliate on margin, glabrescent outside; petals elliptic, 1.5–2.2 by 1.2–1.5 mm, margin entire, apex rounded, glabrous outside, rough and papillose inside; disc lobes semi-orbicular to nearly lanceolate, c. 0.5 by 0.5 mm, apex rounded, glabrous; stamens 5, androphore c. 0.5 mm long, 5-cleft at the top, anthers ovoid to ellipsoid, c. 0.6 mm long, free, thecae slightly divaricate at apex, connectives apically with numerous droplets (expanded cells) with secretion. Pistillate flowers 2.5–3.5 mm diam; pedicel slightly thickened towards apex, c. 6 mm long, apically 0.7–1 mm diam when flowering, accrescent to 2.5 cm long and apically 2 mm diam when fruiting, glabrous to glabrescent; sepals ovate, 1.4–1.7 by 1–1.5 mm, apex acute, slightly pubescent to glabrescent outside; petals (remnants) nearly elliptic, c. 2.1 by 0.8 mm, glabrous outside, rough and scurfy inside; disc lobes as staminate flowers; ovary 1–1.5 mm diam, densely pubescent; styles indiscernible; stigmas completely bifid, each arm c. 1 mm long, thickened at base, slender and often bent upward. Fruits c. 1 cm diam, appressed pubescent; sepals persistent but not accrescent; wall c. 0.5 mm thick, exocarp partly detaching; columella c. 6.5 mm long. Seeds 4.2–5.5 mm diam, pale brown when dry, hilum heart-shaped or rhombic, c. 1.2 by 1–1.2 mm.

    Distribution — Sumatra (endemic).

  n =  T. beccarii; l = T. balgooyi; « = T. calcicolus; ▲ = T. diffusus; ▼ = T. dipteranthus; u = T. filiformis

    Habitat & Ecology — Flowering and fruiting: September.

    Note — A distinct species with short petiole, inflorescences of short glomerules along an erect rachis and 5 stamens in the staminate flowers. Ridley (1925) described T. beccari and T. longisepalus as separate species but he did admit that these two species were possibly based on two sexes of one plant. Our recent collection R.Y. Yu 169 (L), from the Bogor Botanical Gardens (XI.B.XVII.270-270a, originally from Sumatra), bears both the same staminate and pistillate structures as described in Ridley (1925), and thereby confirms the conspecific status of T. beccari and T. longisepalus.

5. Trigonostemon calcicolus (R.I.Milne) R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon calcicolus (R.I.Milne) R.Y.Yu & Welzen, Blumea 62 (2018) 189, map 3; R.Y.Yu et al., Taxon 68 (2019) 928. — Trigonostemon polyanthus Merr. var. calcicolus R.I.Milne, Kew Bull. 50 (1995) 28, in key, 30, in key, 33, fig. 1. — Type: Chew Wee-Lek 679 (holo K; iso L), Sarawak, 1st Division, Kuching District, Tiang Bekap, Mt. Mentawa. 1° 12' N, 110° 23' E.

Small trees, 3 m tall; flowering branches c. 3 mm diam. Outer bark c. 0.1 mm thick, brownish, pubescent to hirsutellous when young, hairs short and stiff; inner bark c. 0.1 mm thick, dark reddish; wood pale brown to reddish brown. Stipules subulate, c. 0.7 mm long, caducous, hirsutellous. Leaves: petiole 4.6–9 cm long, terete but grooved above, hirsutellous; blade broadly elliptic, 16–23.5 by 7–11.5 cm, base acute to rounded, adaxially 2 glands present but caducous, margin entire or slightly distantly serrate, ciliate, apex acuminate to rounded, upper side dark brown to black (when dry), glabrous, lower side brown (when dry), scarcely pubescent to hirsutellous; midrib slightly raised and glabrous above, distinctly elevated and hirsutellous beneath, nerves 9–13 pairs, slightly raised and hirsutellous beneath, small nerves reticulate, obscure. Inflorescences axillary, unisexual; staminate ones thyrsoid, flowers clustered into few very short cymes (nearly a glomerule) at apex of rachis, rachis 2.5–5 cm long, 0.6–0.9 mm diam, hirsutellous; bracts to glomerules elliptic to lanceolate, 7–15 by 1.5–5 mm, apex acute to acuminate, hirsutellous outside, bracts to the flowers small, triangular to lanceolate, c. 0.3 by 0.1 mm, hirsutellous outside; pistillate inflorescences similar to staminate ones but with fewer flowers, 7–10 cm long, 0.7–1.1 mm diam, hirsutellous; bracts to the flowers lanceolate, c. 5 by 1.5 mm, hirsutellous outside. Staminate flowers (unopened) 1.1–1.6 mm diam; pedicel 0.5–2 mm long, 0.3–0.5 mm diam (apex), thickened towards apex, densely hirsutellous; sepals elliptic, 0.5–1 by 0.3–0.5 mm, apex acute to rounded, hirsutellous outside; petals orbicular to elliptic, 0.5–0.6 mm diam, black, glabrous on both sides; disc indiscernible; stamens 5, androphore indiscernible, anthers ellipsoid, c. 0.4 mm long, connectives with apically some droplets (expanded cells) with secretion. Pistillate flowers: sepals triangular, c. 3 by 1 mm, green, thin, pubescent outside; petals elliptic-ovate, c. 1.2 by 1 mm, black, glabrous; disc insignificant; ovary strongly pyriform, c. 0.8 mm diam, glabrous, yellow; stigma slightly divided. Fruits (Milne 1995): oblong-ovate, c. 9 by 8 mm; pedicel c. 10 mm long, pubescent; sepals persistent, puberulous, drying brownish grey. Seeds unknown.

    Distribution — Borneo (Sarawak, endemic).

  « = T. calcicolus; l = T. balgooyi; n =  T. beccarii; ▲ = T. diffusus; ▼ = T. dipteranthus; u = T. filiformis

    Habitat & Ecology — On limestone. Altitude: recorded once from 80 m. Flowering: July.

    Note — The descriptions of the pistillate flowers and fruits are based on Milne (1995). This species is only known from the type collection from Sarawak. The species has the same characteristics of T. villosus var. merrillianus (e.g., long petiole, glomerules on inflorescences), but has 5 instead of 3 stamens. Since the number of stamens is generally reliably constant per species, this taxon is here regarded as a distinct species rather than a variety as it is in Milne (1995).

6. Trigonostemon capillipes (Hook.f.) Airy Shaw (sect. Trigonostemon)

    Trigonostemon capillipes (Hook.f.) Airy Shaw, Kew Bull. 20 (1967) 413; Kew Bull. 26 (1972) 345; Whitmore, Tree Fl. Malaya 2 (1973) 135; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 202; R.I.Milne, Kew Bull. 50 (1995) 28, in key, 29, in key, 45; Chantar., Thai Forest Bull. (Bot.) 33 (2005) 24; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 576; R.Y.Yu & Welzen, Blumea 62 (2018) 191, map 4; R.Y.Yu et al., Taxon 68 (2019) 927; R.Y.Yu & Welzen, Blumea 65 (2020) 29, map 1. — Dimorphocalyx capillipes Hook.f., Fl. Brit. India 5 (1887) 404; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 33; Ridl., Fl. Malay Penins. 3 (1924) 266. — Type: Lobb s.n. (holo K, barcode K000894763), Singapore.

   Trigonostemon sp. nov., aff. indicus (Baill.) Müll.Arg.: Jabl., Brittonia 15 (1963) 168. — Voucher: Kiah 35303 (BO, K, L, SING), Malaysia, Perlis, Bukit Kaki.

Shrubs or small trees, 1–8 m tall; flowering branches 1.7–3.2 mm diam. Bark 0.1–0.2 mm thick, brownish to greyish, slightly pubescent near young parts, smooth; wood pale yellowish. Stipules subulate, 0.5–1 mm long, caducous, pubescent at base. Leaves: petiole 0.3–1(–2.5) cm long, grooved above, pubescent; blade oblanceolate, oblong or obovate, 9–20 by 3–7 cm, chartaceous, base acute to obtuse, with 2 adaxial glands, margin distantly serrate, teeth small, falcate, apex acuminate, upper side glabrous, lower side paler, slightly pubescent and more or less ciliate along margin; midrib slightly raised on both sides, nerves 9–12 pairs, connected along margin, small veins reticulate. Inflorescences: staminate ones thyrsoid, branched (paniculate), 4–8 cm long, glabrescent, axillary or cauliflorous; bracts leaf-like, elliptic to oblong, up to 10 by 4 mm, slightly pubescent abaxially; pistillate inflorescences cymose, peduncles slender, 1–15 cm long, 0.2–0.5 mm diam, often only one flower at top (sometimes with few depauperate flowers below); bracts as in staminate inflorescences, 4–20 by 1–5 mm. Staminate flowers c. 6 mm diam; pedicel 0.2–0.4 cm long, 0.1 (middle part)–0.2 (top) mm thick, glabrescent or slightly pubescent; sepals elliptic, c. 1.6 by 1.2 mm, pale green, apex rounded or slightly notched, under the notch often with a gland on outside surface, but sometimes faint or only a few expanded cells; petals elliptic or spathulate, 3–3.5 by 1.5–1.8 mm, base narrowed, acute to cuneate, sometimes claw-like, entire, apex rounded, dark purple, in mature flowers with an orange flame-like honey mark in the middle of the lower part, smooth and glabrous outside, rough and papillose inside; disc lobes almost obtrapezoid, c. 0.35 by 0.3 mm, c. 0.1 mm thick, apex thickened and slightly reflexed, glabrous; stamens 5, androphore c. 0.6 mm long, c. 0.2 mm diam, 5-branched at c. 0.1 mm below apex, filaments c. 0.1 mm long, anthers c. 0.7 mm long, pinkish, divaricate, connectives apically with numerous dark reddish droplets (or expanded cells) with secretion. Pistillate flowers c. 1 cm diam, pedicel slightly thickening towards apex, 6–9 mm long, apically c. 0.7 mm diam when flowering, in fruit accrescent to 1.5 cm long and apically c. 2 mm diam, slightly pubescent; sepals oblong to lanceolate, c. 4 by 2 mm when flowering, accrescent to 5–15 by 2–6 mm in fruit, pale green, margin slightly serrate, teeth glandular, apex acute to acuminate; petals as staminate flowers but larger, c. 5 by 2 mm; disc lobes rectangular, c. 0.4 by 0.6, apex truncate, corners rounded; ovary c. 1 mm diam, densely hairy, style c. 0.1 mm long, often indistinct, stigmas nearly completely divided, c. 0.9–1 mm long, free arms c. 0.8 mm long, slightly thickened abaxially. Fruits c. 1.2 cm diam, finely hairy; sepals and stigmas persistent, stigmas flattened at base, abaxially hairy; wall c. 0.4 mm thick, exocarp not detaching; columella c. 5 mm. Seeds c. 6 mm diam; hilum heart-shaped, 1–1.6 by 1.4–1.5 mm.

    Distribution — Thailand, Malay Peninsula.

    l= T. capillipes; «=  T. detritiferus; n= T. flavidus

    Habitat & Ecology — Lowland rainforest to mangrove forest. Altitude: 0–300 m. Flowering: December to April; fruiting: December to February.

    Note — Airy Shaw (1967) transferred this species from Dimorphocalyx (now a synonym of Tritaxis) to Trigonostemon without any information on staminate flowers in the type collection. Nevertheless, it can be recognized by the often single-flowered pistillate inflorescences and much enlarged sepals in pistillate flowers, and it differs from the newly proposed Philippine species T. victoriae by having thyrsoid staminate inflorescences and 5 instead of 3 stamens.

7. Trigonostemon detritiferus R.I.Milne (sect. Trigonostemon)

    Trigonostemon detritiferus R.I.Milne, Kew Bull. 49 (1994) 446, Fig. 2; Kew Bull. 50 (1995) 27, in key, 28, in key; R.Y.Yu & Welzen, Blumea 62 (2018) 191, fig. 4, map 4; R.Y.Yu et al., Taxon 68 (2019) 927. — Type: J. Dransfield 6913 (holo K; iso BRUN), Brunei, Teburong District, Selapon.

Small trees, up to 2.5 m tall, 5–12 mm diam, without branches, adventitious roots present at the top of the main branch, 0.2–0.5 mm thick, much branched and curly, dirty and puberulent. Outer bark 0.3–0.4 mm thick, brownish; inner bark 0.5–0.6 mm thick, dark reddish, sap reddish; sapwood c. 1.6 mm thick, yellowish; heartwood c. 2.5 mm diam. Stipules subulate, c. 1.3 by 0.5 mm, pubescent, caducous. Leaves clustered on top of the stem; petiole 0.4–1 cm long, 2–2.5 mm diam, wrinkled and slightly pubescent, upper side flat, lower side rounded; blade oblanceolate, 20–45 by 5.5–10 cm, chartaceous, base rounded to cuneate, adaxial glands not seen, margin distantly serrate, teeth falcate, apex acuminate to almost caudate, upper side glabrous, lower side paler, densely pubescent on especially the venation; venation penninerved, midrib robust, slightly raised on both sides, nerves 15–30 pairs, curved, veins scalariform, veinlets reticulate. Inflorescences: staminate ones flowers single and cauliflorous, axillary, on upper part of branch, or thyrses inserted at leaf axils, 1–7 cm long, few-branched and few-flowered, rachis appressed puberulous; bracts linear to lanceolate, 2–20 by 0.3–6 mm, puberulent; pistillate ones single, inserted at leaf axils. Staminate flowers: pedicel up to 4 mm long; sepals elliptic, 1–1.5 by 0.5–0.8 mm, pubescent outside, glabrous inside; petals obovate, 2–3 by 1–1.8 mm, apex rounded, reddish purple, glabrous; disc glandular, yellowish, c. 0.15 diam; stamens 3, androphore c. 0.5 mm long, anthers pinkish, ellipsoid, 0.4–0.5 mm long. Pistillate flowers: pedicel up to 3.5 cm long, puberulous; sepals and petals as in staminate flowers; disc glands glandular, c. 0.15 mm diam; ovary 0.25–1 mm diam, glabrous to pubescent; styles trifid, indistinct, stigmas slightly to deeply bifid. Fruits c. 6 mm diam, sometimes only one locule mature, other two aborted. Seeds opalescent when young, dark brownish when mature, marbled. Seedling: cotyledons 2, sessile, round, light green, triplinerved. First true leaf subsessile, obovate, base cordate, apex acute, blade light green.

    Distribution — Borneo (Temburong District of Brunei, endemic).

    «= T. detritiferus; l= T. capillipes; n= T. flavidus

    Habitat & Ecology — Primary mixed dipterocarp forest, near rivers (c. 30–300 m away from river bank). Flowering and fruiting: June to November.

    Notes — 1. The species strongly resembles T. wetriifolius in the growing habit, cauliflorous flowers and adventitious roots, while the distinct differences lie in the dark reddish (versus pale yellowish in T. wetriifolius) petals and 3 (versus 5 in T. wetriifolius) stamens.

    2. This species has a special living strategy (also seen in T. wetriifolius, see Airy Shaw & Ng 1978). The leaves are always clustered on the top of the main branch, where the adventitious roots also generate, thus the leaves accumulate dirt and fallen leaves from inside and form humus, from which the nutrition can be absorbed by the adventitious roots.

8. Trigonostemon diffusus Merr. (sect. Trigonostemon)

    Trigonostemon diffusus Merr., Sarawak Mus. J. 3 (1928) 525; Jabl., Brittonia 15 (1963) 164; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key, 46; R.Y.Yu & Welzen, Blumea 62 (2018) 194, map 3; R.Y.Yu et al., Taxon 68 (2019) 927. — Type: Mjöberg 145 (BM, K, UC), Sarawak, Mount Poi.

Shrubs or small trees, at least up to 6 m tall; flowering branches terete, 2–2.5 mm diam. Outer bark c. 0.1 mm thick, pale, slightly hirsute in young parts, glabrous and wrinkled in older parts; inner bark c. 0.2 mm thick, reddish brown; wood pale yellowish. Stipules falcate, 0.6–1 mm long, pubescent. Leaves: petiole 1–9 cm long, slightly pubescent, grooved above, thickened at base and top; blade oblong, 12–19 by 3.5–5.5 cm, membranous, sometimes slightly asymmetric, base acute and often with 2 adaxial glands, margin distantly crenate-dentate, teeth somewhat nipple-like, apex acuminate to caudate, surfaces olive-green, glabrous above and slightly hirsute beneath; midrib raised on both sides, slightly hirsute beneath, nerves 10–12 pairs, veins reticulate. Inflorescences paniculate, large and diffuse, much developed and branched but few flowers present, up to 35 cm long, slightly hirsute; bracts triangular, up to 0.6 by 0.3 mm, abaxial surface slightly pubescent. Staminate flowers (unopened) caducous, c. 1.7 mm diam; pedicel 2–3 mm long, 0.1–0.2 mm diam, glabrescent; sepals elliptic to ovate, 0.9–1.2 by 0.8–1 mm, slightly pubescent outside; petals elliptic, c. 1.5 by 1 mm, dark red or purple, margin slightly ciliate, apex rounded, both sides glabrous; disc lobes almost trapezoid, c. 0.2 by 0.3 mm; stamens 3, androphore c. 0.5 mm long, anthers ellipsoid, c. 0.6 mm long, connectives apically with numerous droplets with secretion. Pistillate flowers and fruits unknown.

    Distribution — Borneo (Sarawak, endemic).

  ▲ = T. diffusus; l = T. balgooyi; n =  T. beccarii; « = T. calcicolus; ▼ = T. dipteranthus; u = T. filiformis

    Habitat & Ecology — Forests near the foot of mountains. Altitude: 760 m. Flowering: September.

   Notes — 1. The species is only known from two collections (the type and J.W. Purseglove P. 4702). It is mainly distinguished by its large, diffuse, few-flowered inflorescences.

    2. Trigonostemon diffusus subsp. condensus, should be synonymised under T. polyanthus, see note 3 under T. polyanthus.

9. Trigonostemon dipteranthus Airy Shaw (sect. Trigonostemon)

    Trigonostemon dipteranthus Airy Shaw, Kew Bull. 20 (1966) 47; R.Y.Yu & Welzen, Blumea 62 (2018) 194, map 3; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: Korthals s.n. (‘853’) (holo L), Sumatra,West Coast Res., Padang Region.

Small trees, 4.5–6 m tall; flowering branches terete or wrinkled, 3–3.5 mm diam, slightly pubescent when young, glabrescent when mature. Outer bark smooth, pale brownish; inner bark c. 0.2 mm thick; wood white. Stipules falcate or subulate, 0.5–1 mm long, often pubescent. Leaves: petiole terete but sometimes slightly grooved above, 3–12.5 cm long, middle part 1–1.5 mm diam, more or less pubescent, often slightly thickened at base and apex; blade oblong to elliptic or slightly oblanceolate, 15–22 by 4.5–8 cm, membranous, base acute or narrowed rounded, margin slightly distantly crenate-serrate, teeth often small, nipple-like or falcate, apex caudate, tip 1.5–2.5 cm long, upper side glabrous, lower side pubescent and paler; midrib flat and glabrescent above, elevated and pubescent beneath, nerves 10–12 pairs, curved and narrowed along margin, pubescent beneath, veins reticulate. Inflorescences axillary bisexual glomerules; peduncles slender, 2–6.5 cm long, finely appressed pubescent, flowers densely clustered at the top of peduncles and subtended by 2 conspicuous bracts; bracts opposite, almost sessile, widely ovate, 2–3.5 by 1.3–2.4 cm, membranous, base rounded or slightly emarginate, margin nearly entire, apex apiculate or acute, upper side glabrous, lower side appressed puberulent, especially along nerves. Staminate flowers c. 6 mm diam; pedicel c. 2 mm long, c. 0.3 mm diam, glabrescent; sepals elliptic, c. 1.2 by 0.6 mm, base connate, apex acute, sparsely puberulent outside; petals obovate, c. 3.5 by 2 mm, reddish brown when dry, base cuneate, apex rounded; disc lobes rectangular, sometimes obtrapezoid, c. 0.15 by 0.2 mm, corners obtuse, membranous, glabrous, apex truncate; stamens 5, androphore c. 1 mm long, 5-cleft at top, filaments c. 0.5 mm long, anthers separate, oblong, c. 0.7 mm long. Pistillate flowers rare, c. 6–8 mm diam; pedicel 3.5–4 mm long, apically c. 0.8 mm thick, densely pubescent; sepals oblanceolate to oblong, 6–7 by 2–3 mm, foliaceous and accrescent in fruit, apex acute to acuminate, pubescent outside, especially near base and along midrib; petals not seen, fallen; disc lobes wide semi-orbicular or rectangular, c. 0.5 by 0.7 mm, slightly folded in the middle; ovary c. 1.5 mm diam, densely pubescent; styles not seen, fallen. Fruits and seeds not seen.

    Distribution — Sumatra (endemic).

  ▼ = T. dipteranthus; l = T. balgooyi; n =  T. beccarii; « = T. calcicolus; ▲ = T. diffusus; u = T. filiformis

    Note — This species is characterized by the glomerules subtended by 2 large, leaf-like bracts. Detailed locality of the type collection, Korthals ‘853’, is based on Airy Shaw (1966).

10. Trigonostemon filiformis Quisumb. (sect. Trigonostemon)

    Trigonostemon filiformis Quisumb., Philipp. J. Sci. 41 (1930) 328, fig. 7; R.Y.Yu & Welzen, Blumea 62 (2018) 194, map 3; R.Y.Yu et al., Taxon 68 (2019) 927; Blumea 65 (2020) 13, fig. 1, map 1. — Type: M.S. Clemens 16751 (holo PNH, †; iso A, NY), Philippines, Luzon, Isabela Prov., Mount Moises.

Small trees; flowering branches 1.5–3.5 mm diam. Outer bark c. 0.1 mm thick, brownish to greyish, smooth, pubescent in young parts; inner bark c. 0.1 mm thick, reddish, sap light red; wood yellow or white. Stipules small, subulate, 0.5–1 mm long, pubescent. Leaves: petiole 1–3(–4.5) cm long, 0.6–1 mm diam, terete, sometimes angled, or furrowed above, pubescent; blade linear to long lanceolate, 13–22 by 0.8–1.5 cm, chartaceous, base acute to cuneate, with 2 adaxial, falcate glands, margin distantly serrate, teeth glandular, apex acuminate to caudate, upper surface dark green, glabrous, lower surface paler, softly appressed pubescent; midrib plain above and slightly raised and densely pubescent beneath, nerves obscure, 10–13 pairs, curved to almost right angled, connected, pubescent beneath, veins reticulate, very vague. Inflorescences terminal or axillary, racemes or thyrses (but often only 1 flower developed on each node); rachis slender, 2–6(–13) cm long, 0.15–0.4 mm diam, pubescent; bracts lanceolate or oblong, 2–10 by 0.3–1.3 mm, slightly pubescent. Staminate flowers: sepals obovate to round, c. 1.5 by 0.5 mm; petals c. 2 by 1.25 mm diam; disc unknown; stamens 3, anthers sessile, erect, globose. Pistillate flowers 3.5 (unopen)–7.5 (post-anthesis) mm diam; pedicels slightly thickened towards apex, 6–9 mm long, apically 0.8–1.1 mm diam, pubescent; sepals elliptic, 2.3–3 by 0.8–1.2 mm, accrescent to at least 9 by 2.2 mm, pubescent outside; petals oblong to oblanceolate, c. 4 by 1.25–1.5 mm, purple, glabrous; disc unknown; ovary at least 0.7 mm diam, densely pubescent; styles often indistinct, trifid; stigmas deeply bifid into 2 arms, each arm 0.6–1.2 mm long. Fruits and seeds unknown.

    Distribution — Borneo (Sabah) and Philippines (Luzon).

  u = T. filiformis; l = T. balgooyi; n =  T. beccarii; « = T. calcicolus; ▲ = T. diffusus; ▼ = T. dipteranthus

    l = T. filiformis; p = T. merrillii; n = T. palustris; « = T. victoriae

    Habitat & Ecology — Lowland forest edge, ultramafic soil in Sabah. Flowering: April and December.

    Notes — 1. The staminate flowers are not seen by us. The description is based on Quisumbing (1930).

    2. The species is distinct from T. verticillatus var. salicifolius by the staminate flowers with 3 instead of 5 stamens. Another useful character is that T. verticillatus var. salicifolius often has two pairs of adaxial glands at leaf base, whereas T. filiformis always has one.

    3. The type was collected from Mt Moises of the Philippines, as was the type of T. stenophyllus Quisumb. Both these two species are poorly known and probably they are conspecific, but this cannot be confirmed until further material is available of both species.

11. Trigonostemon flavidus Gagnep. (sect. Trigonostemon)

    Trigonostemon flavidus Gagnep., Bull. Soc. Bot. France 69 (1922) 749; in Lecomte, Fl. Indo-Chine 5 (1925) 320; P.T.Li & M.G.Gilbert in C.Y.Wu, P.H.Raven & D.Y.Hong, Fl. China 11 (2008) 273; R.Y.Yu & Welzen, Blumea 62 (2018) 194, map 4; R.Y.Yu et al., Taxon 68 (2019) 927; R.Y.Yu & Welzen, Blumea 65 (2020) 33, fig. 2, map 7. — Type: F.J. Harmand 3273 (holo P), Laos: in Lakhon mountains, near Me-Kong.

    Trigonostemon heterophyllus Merr., Lingnan Sci. J. 9 (1930) 38; H.S.Kiu, Fl. Reipubl. Popul. Sin. 44(2) (1996) 163; Chantar., Thai Forest Bull. (Bot.) 33 (2005) 24; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 577, Plate 31: 1. — Syntypes: W.T. Tsang 594 (B, BM, BO, K, L, MO, NTUF, NY, P); W.T. Tsang 17343 (PE, US); both China, Hainan, Danzhou County (Taam Chau District), Mt. Sha Bao (Sha Po Shan).

Evergreen, small trees, 1–2.5 m tall; flowering branches up to 4 mm diam, grey, densely hirsute. Bark c. 0.3 mm thick, smooth or roughened; wood reddish brown. Stipules subulate, c. 0.7 mm long, hirsute around base. Leaves: petiole terete but sometimes flattened or grooved above, 0.2–1.2 cm long, densely hirsute; blade obovate or oblanceolate, sometimes unequal, unevenly narrowed in the lower middle part, 9–35 by 5–9 cm, thin chartaceous or membranous, base abruptly rounded, with 2 adaxial glands, margin distantly serrate, teeth small and nipple-like, apex caudate to acuminate, dark green above and dull light green underneath, hirsute on both sides, especially on nerves and margin; midrib thin, elevated on both sides, nerves 10–12 pairs, veins reticulate, often obscure. Inflorescences bisexual, cauline, usually in short cymes or thyrses, 1–3 cm long, hirsute, often bracteate under nodes or flowers; bracts lanceolate to linear, up to 4 by 0.6 mm. Staminate flowers c. 6 mm diam; pedicel c. 3.5 mm long, c. 0.2 mm thick, pinkish, glabrous; sepals elliptic or obovate, c. 2 by 1 mm, base connate, margin ciliate, apex acute, hirsute outside, glabrous inside; petals obovate, 4–4.5 by 2–2.5 mm, base claw-like, apex rounded, glabrous, dark reddish to maroon-purple; disc glands elliptic or obovate, c. 0.5 by 0.25 mm, narrowed at base and slightly reflected at apex, light orange, glabrous; stamens 3, androphore c. 1 mm long, c. 0.1 mm diam, shortly trifid at top, filaments c. 0.2 mm long; anthers free, divaricate at top, each theca 0.4–0.5 mm long, connective with apically numerous droplets with secretion. Pistillate flowers few, slightly enlarged when fruiting, up to c. 1 cm diam; pedicel (in fruiting flower) c. 7 mm long, thickened towards apex to up to 1 mm diam; sepals long lanceolate to linear, c. 2.5 by 1.2 mm when flowering, accrescent to up to 7.5 by 2 mm in fruit, margin with a few teeth, apex acuminate, outside hirsute, inside glabrous; petals not seen, fallen; disc glands rectangular to semi-orbicular, c. 0.5 by 0.4 mm, rounded or truncate at apex, glabrous; ovary c. 3.5 mm diam, bright dark green, densely hirsute, styles almost indistinct, stigmas 3, completely divided. Fruits c. 1.2 mm diam, green, densely hirsute; wall woody, c. 5 mm thick; columella c. 5 mm long. Seeds c. 6.5 by 5.5 mm, dark brownish when dry, hilum irregularly shaped, more or less triangular, c. 1.5 mm diam.

    Distribution — India, China, Laos, Thailand, Malay Peninsula.

    n= T. flavidus; l= T. capillipes; «= T. detritiferus

    Habitat & Ecology — Understorey in evergreen forest to deciduous hardwood or bamboo forest, often near rivers, growing on sandstone to conglomerate bedrock. Altitude: c. 200 m. Flowering: January to March; fruiting: February, July to October.

    Note — Trigonostemon flavidus is tentatively treated as a separate species here, but it strongly resembles T. semperflorens from India, of which it might be a synonym. It differs by having more hairs on the upper leaf surfaces.

12. Trigonostemon hartleyi Airy Shaw (sect. Tylosepalum)

    Trigonostemon hartleyi Airy Shaw, Kew Bull. 33 (1979) 535; Kew Bull., Addit. Ser. 8 (1980) 206; R.Y.Yu & Welzen, Blumea 62 (2018) 195, map 1; R.Y.Yu et al., Taxon 68 (2019) 930. — Type: Hartley 11087 (holo BRI; iso L), Papua New Guinea, Morobe Dist., S of the Busu River, about 19 km N of Lae.

Small trees, up to 3.5 m tall; flowering branches terete, c. 3.8 mm diam, pale grey, young part appressed pubescent. Outer bark c. 0.1 mm thick, light grey, smooth; inner bark c. 0.1 mm thick, reddish; sap clear, yellowish; wood whitish. Stipules subulate, c. 1 mm long, pubescent at base. Leaves clustered at apex of branchlets; petiole terete but grooved above, 1.5–3 cm long, c. 1.5 mm diam, glabrescent or appressed pubescent near base and apex when young; blade elliptic to obovate, 14–20 by 5–8 cm, thin chartaceous, base and apex acute, base with two adaxial glands, often subulate or nipple-like, margin subentire or slightly crenate or dentate, teeth falcate or often obscure, above dark green, underneath pale green glaucous, both sides glabrous or slightly pubescent when young; midrib flat above, raised beneath, nerves 7–9 pairs, veinlets reticulate, very thin and obscure. Inflorescences: staminate ones c. 2 cm long, few-flowered; primary rachis c. 1 cm long, c. 1 mm thick, glabrous, 2 bracts at apex, c. 1 mm long, subglabrous; secondary rachis 7 mm long, slender and glabrous, apex with few bracts; pistillate inflorescences axillary, often only one open flower present apically, with a few depauperate flowers below; peduncles terete, up to c. 9 cm long, c. 0.8 mm thick, glabrous or slightly pubescent at base, bracteate on each node; bracts lanceolate or triangular, c. 1 by 0.5 mm, pubescent outside. Staminate flowers: pedicel slender, 4–5 mm long; sepals distinctly unequal, wide elliptic or obovate, 1–2 mm long, apex rounded, with few hairs outside; petals wide ovate, c. 3 by 2 mm, orange, base shortly claw-like, apex rounded; disc lobes suborbicular, c. 0.5 mm diam, flat, erect, solid, glabrous, entire, brownish when dry; stamens 5, androphore c. 0.5 mm long, anthers relatively large, ovoid, c. 0.5 mm long, erect, connectives very short. Pistillate flowers c. 7.5 mm diam; pedicel c. 3.5 cm long, thickened towards apex, up to 1.5 mm diam, glabrous; sepals oblong, 1.5–2 by c. 1 mm, not accrescent, apex rounded, greenish, outside slightly pubescent, with one conspicuous gland in the middle; petals not seen, caducous; ovary c. 3.5 mm diam, c. 3 mm high, stigmas 3, very shortly recurved. Fruits 12–15 mm diam, smooth, brownish. Seeds not seen.

    Distribution — New Guinea (Morobe district, endemic).

  l = T. apetalogyne; « = T. hartleyi

    Habitat & Ecology — Rainforest, growing on slope. Altitude: 150 m. Flowering and fruiting: January.

    Note — Descriptions of the staminate inflorescences, staminate flowers and ovary are based on Airy Shaw (1979). Only known from the type, Hartley 12211 (K, paratype) and a doubtful collections (Hartley 9811, K). The species is different from T. apetalogyne only by having 5 instead of 3 stamens (see also note under latter).

13. Trigonostemon laevigatus Müll.Arg. (sect. Tylosepalum)

    Trigonostemon laevigatus Müll.Arg., Flora 47 (1864) 538; in A.DC., Prodr. 15, 2 (1866) 1111; Boerl., Handl. Fl. Ned. Ind. 1 (1900) 232, 284; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 94; Merr., J. Straits Branch Roy. Asiat. Soc., Spec. No. (1921) 345 (2nd mentioning, first = Microdesmis caseariifolia Planch., see Jablonski, Brittonia 15, 1963: 168); Ridl., Fl. Malay Penins. 3 (1924) 265; Jabl., Brittonia 15 (1963) 167; Airy Shaw, Kew Bull. 26 (1972) 346; Whitmore, Tree Fl. Malaya 2 (1973) 135; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 203; Kew Bull. 32 (1978) 417; Kew Bull. 36 (1981) 355; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; Chantar., Thai Forest Bull. (Bot.) 33 (2005) 25; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 578, Fig. 93; R.Y.Yu & Welzen, Blumea 62 (2018) 195, fig 5, map 5; R.Y.Yu et al., Taxon 68 (2019) 930; R.Y.Yu & Welzen, Blumea 65 (2020) 36. — Lectotype (designated by Yu & Welzen 2018): Motley 686 (holo K), Borneo, Bangarmassing. Paratype: Barter s.n. (K, K), Borneo.

    Trigonostemon anomalus Merr., Philipp. J. Sci. 16 (1920) 569; Enum. Philipp. Fl. Pl. 2 (1923) 451. — Type: FB (Villamil) 22018 (holo PNH, †; iso US), Philippines, Mindanao, Zamboanga District, Naganaga.

    Trigonostemon everettii Merr., Philipp. J. Sci. 7, Bot. (1912) 408; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 408; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 451; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 46. — Type: FB (Everett) 7257 (holo PNH, †; iso A), Philippines, Negros, Mount Silay.

    Trigonostemon laevigatus Müll.Arg. var. petiolaris Airy Shaw, Kew Bull. 32 (1978) 417; R.I.Milne, Kew Bull. 50 (1995) 28, in key, 29, in key. — Type: S (Chai) 19224 (holo K; iso L, SAN, SING), Sarawak, Fourth Division, Simpang Tiga, Ulu Mayeng, Kakus.

    Trigonostemon petelotii Merr., Univ. Calif. Publ. Bot. 10 (1924) 425. — Type: Pételot 795 (holo A), Vietnam, Ninh Binh, Cho-Ganh. See note.

    Trigonostemon sp. nov., aff. chinensis Merr.: Jabl., Brittonia 15 (1963) 168. — Voucher: KEP (Strugnell) 20275 (K, KEP, SING), Malaya, Pahang, Ulu Gali Raub. See note.

    Trigonostemon sp. nov., aff. chinensis Merr.: Jabl., Brittonia 15 (1963) 168. — Voucher: van Steenis 910 (BO, L, SING), Sumatra, Anambas Islands, Siantan Island, E of Terimpa. See note.

Trees, 5–15 m tall, stem up to 15 cm diam; flowering branches 1.5–2 mm diam, often slightly pubescent near nodes and apical buds. Bark 0.3–0.5 mm thick, smooth, lenticellate, light greenish to pale or dark brownish to blackish; sap red, pink or colourless; wood whitish to reddish brown, with brownish pink rays. Stipules falcate to nipple-like, 0.3–1 mm long, pubescent, caducous, often obscure or not seen. Leaves: petiole terete but often flat or grooved above, 0.5–1.5(–4) cm long, wrinkled, glabrescent to pubescent, base and apex sometimes pulvinate; blade elliptic, sometimes oblong, ovate or oblanceolate, 6–20 by 2.5–8 cm, chartaceous or coriaceous, base acute to cuneate, with 2 adaxial glands, margin entire, apex acuminate to caudate, above greenish, underneath pale green below, both sides glabrous; venation triplinerved, midrib elevated beneath, nerves 6–9 pairs, bow-shaped, narrowed along margin, veinlets reticulate, obscure. Inflorescences terminal or axillary, cymes or paniculate thyrses, abbreviated and condensed or elongated and lax, 0.5–4 cm long, often branched, glabrescent or pubescent, bracts long-triangular to linear, up to 3 by 1 mm, velutinous. Staminate flowers 6–10 mm diam; pedicel c. 1 cm long, c. 0.2 mm thick, scarcely pubescent; sepals oblong to obovate to orbicular, 2–4.5 by 1.8–2.5 mm, sometimes unequal, then outer 2 or 3 larger, imbricate, margin entire, apex rounded, yellowish green, often finely puberulent on both sides, outside also pubescent with longer hairs and sometimes with a subapical gland (var. croceus); petals flabellate and bilobed, each lobe 3–6 by 1.5–3 mm, yellow or reddish, glabrous, few parallel veins visible, base claw-like, apex notched to 1/3 to 1/2 of length and often with a small gland below the notch; disc annular, c. 0.5 mm high, glabrous, apex recurved; stamens 3, androphore 0.3–1.5 mm high, trifid at apex, filaments 0.2–0.5 mm long, anthers oblong, c. 0.8 mm long, yellow, free, base somewhat auriculate, not divaricate at apex. Pistillate flowers c. 6 mm diam, pedicel thickened towards apex, up to 2.5 cm long, apically c. 1 mm thick, slightly pubescent; sepals, petals and disc as in staminate flowers; ovary c. 1 mm diam, greenish, glabrescent to densely hairy, style c. 0.1 mm long, sometimes indistinct, stigmas 3 separate arms, c. 0.6 mm long, c. 0.1 mm thick, apex very slightly thickened and bifid. Fruits c. 1 cm diam, greenish, finely hairy; wall 0.4–0.6 mm thick, exocarp detaching; columella 5–6.5 mm long. Seeds 7–8 by 6–7 mm; hilum 1.5–3 by 1–2 mm.

    Distribution — Vietnam, Thailand, Malay Peninsula, Sumatra, Java, Borneo, Philippines, Lesser Sunda Islands.

    Note — The species is wide-spread and is often recognized by its short petiole, hairy sepals, and often flabellate and bilobed petals. The last three synonyms are only tentatively treated here because of the inadequate material.

Key to the varieties

 

1a.	Sepals without a gland outside	a. var. laevigatus
1b.	Sepals with a gland outside	b. var. croceus

 

a. var. laevigatus

 

    Trigonostemon laevigatus Müll.Arg. var. laevigatus: R.Y.Yu & Welzen, Blumea 62 (2018) 197, fig. 5, map 5; Blumea 65 (2020) 36, map 9.

 

 

Sepals without a gland outside.

    Distribution — As the species.

 

   l = T. laevigatus var. laevigatus; «= T. laevigatus var. croceus

 

    Habitat & Ecology — Mixed lowland dipterocarp forest, growing on clay to sandy soils to basalt derived soils of hill slopes. Altitude: 30–600 m. Flowering: all year round; fruiting: April, August, September, November.

    Vernacular name — Borneo: Mampan (Banjar-Malay).

    Notes — 1. The variety generally has a short petiole (often shorter than 1.5 cm) but it can be up to 4 cm long in some populations (e.g., in some populations from Brunei and Sabah). Since the variance is continuous, Airy Shaw’s var. petiolaris is synonymised here.

    2. The sepals often have 2 layers of hairs on the outside, the relatively stiffer and longer hairs form the upper layer and often a layer of very dense and fine hairs that forms the lower layer and which is also present on the inside.

 

b. var. croceus (B.C.Stone) R.Y.Yu & Welzen

 

    Trigonostemon laevigatus Müll.Arg. var. croceus (B.C.Stone) R.Y.Yu & Welzen, Blumea 62 (2018) 197, map 5; Blumea 65 (2020) 37, map 9. — Trigonostemon croceus B.C.Stone, Malaysian Forester 43 (1980) 289. — Type: Stone 9586 (holo KLU; iso K, L), Malaysia, Selangor, on the Pahang border at Genting Sempah.

 

Sepals with a gland outside.

    Distribution — Thailand, Malay Peninsula.

 

   «= T. laevigatus var. croceus; l = T. laevigatus var. laevigatus

 

    Habitat & Ecology — Hill evergreen forest to grassy sites. Altitude: 900–1300 m. Flowering: November to May.

    Note — Stone (1980) newly described T. croceus, because it had 5 instead of the 3 stamens of T. laevigatus. We dissected one staminate flower from the isotype and it turned out to have 3 stamens. Its only difference from the typical T. laevigatus are the showy, protruding glands on the sepals, but there is a continuous variation from being glandless to having a flat gland to even having a protruding gland. However, according to the specimen notes the croceus form occurs at higher altitudes than the typical laevigatus form. Therefore, T. croceus is here regarded as a variety of T. laevigatus.

 

14. Trigonostemon longifolius Wall. ex Müll.Arg. (sect. Spinipollen)

    Trigonostemon longifolius Wall. [ex Baill., Étude Gén. Euphorb. (1858) 341, nom. inval., still nom. nud.] ex Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1108; Kurz, For. Fl. Burma 2 (1877) 406 (‘longifolium’); Hook.f., Fl. Brit. India 5 (1887) 396; Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii (1911) 88, fig. 28; Ridl., Fl. Malay Penins. 3 (1924) 264; Jabl., Brittonia 15 (1963) 162; Airy Shaw, Kew Bull. 26 (1972) 347; Whitmore, Tree Fl. Malaya 2 (1973) 136; Airy Shaw, Kew Bull. 36 (1981) 355; Chantar., Thai Forest Bull. (Bot.) 33 (2005) 26; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 579, fig. 94; R.Y.Yu & Welzen, Blumea 62 (2018) 197, fig. 6, map 6; R.Y.Yu et al., Taxon 68 (2019) 929; R.Y.Yu & Welzen, Blumea 65 (2020) 37, map 10. — [Croton longifolius Wall., Numer. List (1847) 7717, nom. nud., non Müll.Arg., Fl. Bras. 11(1873) 170.] — Lectotype (designated by Yu & Welzen 2018): Wallich 7717 (K, barcode K000959328; iso G, K, barcode K000959327), Malaya, Penang Island. Paratypes: Griffith KD 4798 (K), India,Tenasserim and Andamans; Griffith KD 4797 (K), Malaya, Malacca.

    ?Athroisma dentatum Griff., Notul. 4 (1854) 478 (‘dentatis’); Ic. Pl. Asiat. 4 (1854) pl. 585, fig. 4. — Type: Griffith s.n.?, Nov. 1834 (K?), Mergue, Madamaca (see Hook.f. 1887: 396; Pax & Hoffmann 1911: 88).

    ?Athroisma serratum Griff., Notul. 4 (1854) 477 (‘serratis’); Ic. Pl. Asiat. 4 (1854) pl. 585, fig. 9. — Type: Griffith s.n.? (K?), Mergue, Tenasserim (see Airy Shaw 1972: 347).

    Croton longipedunculatus Elmer, Leafl. Philipp. Bot. 1 (1908) 311. — Trigonostemon longipedunculatus (Elmer) Elmer, Leafl. Philipp. Bot. 4 (1911) 1306; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 408; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.I.Milne, Kew Bull. 50 (1995) 38. — Type: Elmer 7264 (holo PNH, †; iso BO, G, K), Philippines, Leyte, Prov. of Leyte, Palo.

    Trigonostemon oblanceolatus C.B.Rob., Philipp. J. Sci. 6, Bot. (1911) 337; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 407; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47. — Type: Williams 2185 (holo PNH, †; iso K, NY, US), Philippines, Mindanao, Zamboanga District, Sax River.

    Prosartema gaudichaudii Gagnep., Bull. Soc. Bot. France 72 (1925) 468., non Trigonostemon gaudichaudii (Baill.) Müll.Arg. (1865). — Trigonostemon gagnepainianus Airy Shaw, Kew Bull. 32 (1978) 415. — Syntypes: Gaudichaud 167 (P), Vietnam, Tourane; Poilane 8306 (P), Vietnam, from Nhatrang to Ninh Hoa; Poilane 10220 (P), Vietnam, prov. de Quang Tri, Mai-lanh; Poilane 10446 (P, K), Vietnam, Prov. de Quang Tri, Dent du Tigre. 

    Trigonostemon sanguineus auct. non Gagnep.: Ridl., Bull. Misc. Inform. Kew (1926) 80. — Trigonostemon ridleyi Jabl., Brittonia 15 (1963) 165, Fig. 8. — Type: Boden-Kloss 14697 (holo SING; iso K), Sumatra, Sipora Island of Mentawi Group.

    Trigonostemon elmeri Merr., Pl. Elmer. Born. (1929) 162; Jabl., Brittonia 15 (1963) 162; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 202; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key, 41. — Type: Elmer 20936 (holo PNH, †; iso BM, BO, K, L, 2 sheets, SING, U), Sabah, near Tawao.

    Trigonostemon howii Merr. & Chun, Sunyatsenia 2 (1935) 262; H.S.Kiu, Fl. Republ. Popul. Sin. 44(2) (1996) 163. — Type: F.C. How 70940 (A, IBSC, K, NY, US), China, Hainan.

    Trigonostemon ionthocarpus Airy Shaw, Kew Bull. 21 (1968) 407; Kew Bull., Addit. Ser. 4 (1975) 203; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key. — Type: SAN (Meijer) 19672 (holo K; iso SING), Sabah, Sandakan Dist., Mile 17, Gum-Gum.

    Trigonostemon matangensis R.I.Milne, Kew Bull. 49 (1994) 445, fig. 1; Kew Bull. 50 (1995) 27, in key, 29, in key. — Type: Ridley s.n. (holo K), Sarawak (SW), 1st Division, Matang.

    Trigonostemon longipedunculatus (Elmer) Elmer var. mollis R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key, 40. — Type: SAN (James Ah Wing) 38218 (holo K; iso L, SAN), Sabah, Sandakan District, Sekong Kechil, Sepagaya, Sandakan Bay.

Small trees, 1–5 m tall, stem up to 7 cm diam; flowering branches 2–5(–7) cm diam. Outer bark 0.1–0.25 mm thick, smooth, pubescent to hispid when young, whitish to brownish; inner bark 0.2–0.4 mm thick, yellowish to reddish brown, soft; sapwood 0.8–1.5 mm thick, white to dark brownish; heartwood 2–3 mm diam. Stipules linear to hook-like, 2–8.5 by 0.3–1 mm, often pubescent. Leaves: petiole terete, 0.4–3.5 cm long, often wrinkled, hispid; blade oblanceolate, (10–)12–28(–46) by (2.8–)4–10(–15) cm, membranous to chartaceous to coriaceous, base cuneate to round, margin distantly serrate, apex acuminate to slightly caudate, upper side glabrous to slightly pubescent, lower side often pubescent to hispid; midrib robust, elevated on both sides, nerves (9–)11–16(–33) pairs, often slightly curved and connected along margin, veins scalariform, veinlets reticulate. Inflorescences uni- or bisexual, axillary or terminal, loose or condensed, per node a single flower or short cymes, rachis (7–)15–30(–55) cm long, 0.5–4 mm diam, pubescent; bracts lanceolate to linear, 3–8 by 0.3–1 mm, pubescent. Staminate flowers 4–5 mm diam; pedicel 1.5 (Thailand, Malay Peninsula, Sumatra)–5 (Borneo) mm long, 0.1–0.2 mm diam, pubescent, base articulate; sepals elliptic, 1.2–2 by 0.7–1 mm, green, margin entire, apex rounded, pubescent outside, glabrous inside; petals spathulate to obovate, 2–2.5 by 1.2–1.7 mm, pinkish to bluish black, base slightly claw-like, sometimes with 2 gland lobes (Thailand, Malay Peninsula, Sumatra), margin entire, apex rounded, smooth outside, often rough and papillose inside; disc annular, 0.2–0.4 mm wide, margin often 5-notched; stamens 3, androphore c. 0.4 mm long, trifid at top, anthers free, divaricate, connective sometimes protruding at top (Thailand, Malay Peninsula, Sumatra). Pistillate flowers 4–5 mm diam; pedicel slightly thickened towards apex, 1.7–3 (Thailand, Malay Peninsula, Sumatra)–9 (Borneo) mm long, apically 0.5–1 mm diam; sepals elliptic to lanceolate, 1.2–1.8 by 0.8–1.5 mm, margin entire, apex rounded to acute, pubescent outside, glabrous inside; petals and disc as staminate flowers; ovary c. 0.7 mm diam, densely pubescent, glabrescent, slightly (Thailand, Malay Peninsula, Sumatra, Borneo, Philippines) to extremely (Borneo) warty; styles short, often indistinct, trifid; stigmas bifid into 2 flattened lobes. Fruits 1.2–1.4 cm diam, green, pubescent, glabrescent, slightly to extremely warty; sepals persistent, not accrescent; wall 0.4–0.6 mm thick, exocarp partly splitting off; columella 5.5–6 mm long. Seeds 6.5–7 by 6–6.5 mm; hilum elliptic to rhombic to heart-shaped, 2–4.5 by 2.5–4 mm.

    Distribution — China, India, Thailand, Vietnam, Malay Peninsula, Sumatra, Borneo, Philippines.

    Habitat & Ecology — Primary to logged forests, flat land to hill sides, sometimes near rivers, growing on black soil or sandy or stoney clay. Altitude: 15–1000 m. Flowering and fruiting: all year round.

    Notes — 1. The staminate flowers are cauliflorous on one specimen (Wenzel 1513, BM).

    2. Most of the species in this complex, now synonymised, were based on slight differences, but all show the same essential similarities including the short petiole, spike-like inflorescences and the more or less warty fruits. All of these indicate that they are conspecific. Two kinds of forms can be distinguished, though there is overlap via intermediates that cannot be placed: a form, often identified as T. elmeri, mostly distributed in Thailand, Malay Peninsula, Sumatra and parts of Borneo with short pedicel (1.5–3 mm long), petals with 2 glands at base and densely hairy but slightly warty fruits; another form, often identified as T. ionthocarpus, mainly in parts of Borneo and the Philippines with longer but thinner pedicel (3–9 mm long), petals with papillate hairs inside but without a basal gland and sometime extremely warty fruits. A molecular phylogeny of this species complex may enlighten an infraspecific distinction between the forms.

15. Trigonostemon longipes (Merr.) Merr. (sect. Trigonostemon)

    Trigonostemon longipes (Merr.) Merr., Philipp. J. Sci. 11, Bot. (1916) 191; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.xiv (1919) 41; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.Y.Yu & Welzen, Blumea 62 (2018) 199, fig. 7, map 7; R.Y.Yu et al., Taxon 68 (2019) 927; Blumea 65 (2020) 16, fig. 2, map 2. — Dimorphocalyx longipes Merr., Philipp. J. Sci. 1, Suppl. (1906) 82. — Lectotype (designated by Yu & Welzen 2018): FB (Whitford) 1066 (lecto K; iso P), Philippines, Luzon, Bataan Prov., Mount Mariveles. Paratypes: FB (Borden) 1801 (BM, BO, K), Philippines, Luzon, Bataan Prov., Mount Mariveles; FB (Merrill) 2699 (BM, K), Philippines, Luzon, Province of Rizal, Bosoboso.

Small trees, up to 4 m tall, stem c. 9 cm diam; flowering branches terete, 2–3 mm diam, glabrous except pubescent near apical buds. Bark c. 0.2 mm thick, pale brownish, smooth, wrinkled; wood pale yellowish. Stipules subulate, 0.5–1 mm long, pubescent. Leaves: petiole terete but grooved above, 1–8 cm long, glabrescent or slightly pubescent; blade oblong, sometimes oblanceolate, 5.5–16 by 2.5–6 cm, coriaceous, base cuneate, with 2 adaxial glands, margin entire or slightly crenate, apex acuminate to somewhat caudate, upper side dark green, lower side light green, both sides glabrous; midrib flat above and elevated underneath, nerves 8–11 pairs, curved and connected along margin, veinlets reticulate, often obscure. Inflorescences often unisexual, axillary or terminal, sometimes cauliflorous, thyrsoid, up to 15 cm long, glabrous or slightly pubescent, part of staminate flowers single and cauliflorous; few glomerules on a long main rachis, each node subtended by 1 bract; latter lanceolate, up to 1.5 by 0.8 mm, often pubescent; glomerules few-flowered (often 5–10 in staminate inflorescences and 1–3 in pistillate ones), bracteate under each flower, lanceolate, up to c. 0.7 by 0.5 mm, densely pubescent. Staminate flowers c. 4 mm diam; pedicel c. 1 mm long, c. 0.45 mm diam, slightly pubescent; sepals orbicular, c. 2 by 2 mm, imbricate, base connate, apex rounded, pubescent outside; petals elliptic, c. 2 by 1 mm, contort, margin sometimes ciliate; disc lobes obovate or semi-orbicular, c. 0.5 by 0.5 mm, c. 0.15 mm thick, glabrous, apex acute; stamens 5, androphore short, often indistinct, anthers c. 0.5 mm long, gathered on the top of androphore. Pistillate flowers c. 6 mm diam; pedicel 2–3 mm long, thickened towards apex, c. 1.2 mm thick; sepals oblong, slightly accrescent in fruit, up to 3.5 by 2 mm, pubescent outside, apex rounded; petals not seen, caducous; disc lobes semi-orbicular, c. 0.5 by 1 mm, glabrous; ovary not seen. Fruits c. 1 cm diam, glabrous; wall c. 0.4 mm thick; columella c. 3 mm long. Seeds c. 6 mm diam.

    Distribution — Philippines (endemic).

   « = T. longipes; ▲= T. lychnos; n (also including l) = T. magnificus; l = T. malaccanus; ▼ = T. merrillii

    Habitat & Ecology — Secondary forest, on clay loam. Altitude: 175–250 m. Flowering: January to April, September; fruiting: January, April.

    Note — The altitude information is based on Merrill (1906). The ovary is probably glabrous because the fruits are glabrous. The species strongly resembles T. verticillatus var. verticillatus in the variable long petiole and the 5 stamens of the staminate flowers, but they are different in their inflorescences: several flowers (often more than 5) cluster into significant glomerules along the main rachis and the internodes are relatively distinct in T. longipes whereas in T. verticillatus var. verticillatus flowers are evenly spread along the spike-like rachis (only 1–3 flowers present per node) and the internodes are very short. A molecular phylogeny may result in a better conclusion about its distinctiveness.

16. Trigonostemon lychnos (R.I.Milne) R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon lychnos (R.I.Milne) R.Y.Yu & Welzen, Blumea 62 (2018) 201, map 7; R.Y.Yu et al., Taxon 68 (2019) 927. — Trigonostemon polyanthus Merr. var. lychnos R.I.Milne, Kew Bull. 50 (1995) 28, in key, 30, in key, 35, fig. 2. — Type: Coode 6766 (holo K; iso BRUN, K, KEP, L), Brunei, Tutong District, near Sungai Liang, Andalau Forest Reserve.

Slender treelets, up to 4 m tall, few branched; flowering branches c. 6 mm diam. Bark pale brownish, slightly pubescent near young parts, smooth when mature; sap red; wood reddish brown, pith loose. Stipules falcate, c. 1 mm long, caducous, pubescent. Leaves: petiole variable, 1–22 cm long (on a single flowering branch), terete, slightly grooved above, slightly pubescent when young, glabrous when mature; blade elliptic, 11–33 by 5.5–23.5 cm, chartaceous to coriaceous, base acute, with 2 adaxial glands, margin distantly serrate, teeth small, glandular, apex acuminate, upper side dark green (when dry), glabrous, lower side brownish (when dry), sparsely pubescent (more hairy on venations), more or less ciliate along margin; midrib slightly raised beneath, nerves 9–10 pairs, small veins reticulate. Inflorescences: staminate ones paintbrush-like, peduncle up to 13.5 cm long, bracts lanceolate, 1–1.6 by 0.5–0.7 cm; pistillate ones paintbrush-like but condensed into glomerules, pendulous; peduncles 20–29 cm long, 1.5–3.4 mm diam, terete, glabrous, base with 2 involucral bracts, as stipules, apex with few bracts subtending the glomerule, apical bracts obovate to lanceolate, 3–8 by 1.8–4.2 cm, base acute to reniform, apex acuminate, green, glabrous on both sides, glabrous or sometimes very sparsely pubescent near base; glomerules (few clustered short cymes) glabrous, with few small bracts under each flower, small bracts amorphous, slightly pubescent. Staminate flowers c. 4.5 mm diam, pedicel 4–7 mm long, very thin; sepals elliptic, c. 1.5 by 1 mm, pale pinkish green; petals long elliptic, c. 3 by 1.2 mm, purple; stamens 3, androphore c. 0.5 mm long, anthers with apically droplets on connective. Pistillate flowers unopen, pedicel covered by bracts, unseen; sepals elliptic, c. 3 by 2 mm; petals purple, elliptic, ovary unknown. Fruits and seeds unknown.

    Distribution — Borneo (Belait and Tutong districts of Brunei, endemic).

   ▲= T. lychnos; « = T. longipes; n (also including l) = T. magnificus; l = T. malaccanus; ▼ = T. merrillii

    Habitat & Ecology — Mixed lowland forest; heath forest on sandy soil (Milne 1995). Altitude: 50 m. Flowering: April.

    Vernacular name — Sagubang kayu (Brunei).

    Note — A distinct species with only a few collections. We regard it as a separate species because of its big difference from T. polyanthus in the variable petiole and blade and the showy subtending bracts under the inflorescences. The variable petiole and leaf-like bracts also resemble T. villosus var. merrillianus.

17. Trigonostemon magnificus R.I.Milne (sect. Trigonostemon)

    Trigonostemon magnificus R.I.Milne, Kew Bull. 50 (1995) 51, Fig. 1 (‘magnificum’) ; R.Y.Yu & Welzen, Blumea 62 (2018) 201, map 7; R.Y.Yu et al., Taxon 68 (2019) 927. — Type: W.J.J.O. de Wilde & B.E.E. de Wilde-Duyfjes 19441 (holo K; iso BO, KLU, L, P), Indonesia, Sumatra, Aceh, c. 75 km WNW of Medan, Gunung Leuser National Park, Sikunder Forest Reserve, Besitang River.

Erect small trees, up to 4.5 m tall; flowering branches 0.8–1 cm diam. Outer bark c. 0.1 mm thick, extremely wrinkled, densely tomentose; inner bark c. 1 mm thick, sap red, sticky; wood yellowish. Stipules subulate, c. 1 mm long, hirsute near base. Leaves: petiole 2.5–9 cm long, 1.7–3 mm diam, tomentellous, wrinkled; blade large, oblong, 18–35 by 7–14 cm, coriaceous, base truncate to acute, often with 2 adaxial subulate glands, margin entire or slightly distantly serrate, apex acuminate, upper side dull green, with a few hairs, lower side very pale, densely tomentose; midrib flat above, elevated and densely tomentose beneath, nerves 14–21 pairs, bow-shaped, veins and veinlets reticulate. Inflorescences bisexual, often axillary, very large panicles, up to 45 cm long, many-flowered, flowers open at same time, pilose; main rachis terete, sometimes angular, 1–2 mm diam, bracteate under each node, bracts linear, up to 8 by 1 mm; secondary and tertiary branches 0.3–0.6 mm thick, often with pistillate flowers above and more staminate flowers below. Staminate flowers small, 3–5 mm diam; pedicel 2.5–3 mm long, c. 0.2 mm diam, pubescent; sepals oblong or lanceolate, 1–2 by 0.5–1 mm, base connate, apex acute to acuminate, often with one globose gland outside, densely sericeous outside and scarcely puberulent inside; petals obovate, c. 3.5 by 1.5 mm, contort, base long cuneate, apex rounded, glabrous outside, rough and slightly papillose inside, dark purplish black; disc glands c. 0.4 by 0.4 mm, somewhat fleshy, apex often recurved; stamens 3, androphore erect, c. 0.8 mm high, anthers ellipsoid, c. 0.5 mm long, free, divaricate at apex. Pistillate flowers larger, c. 6 mm diam, more greenish; pedicel c. 4 mm long, 0.6–0.8 mm diam when flowering, thickened to 1.7 mm and elongated to 4 cm when fruiting, densely hirsutulous; sepals long-triangular or lanceolate, c. 2.5 by 1 mm when flowering, accrescent in fruit to 8.5 by 1.5 mm, with 3 teeth near apex and often with one gland on the tip of each tooth, densely hirsutulous on both sides; petals caducous, as staminate flowers; disc lobes semi-orbicular, c. 0.3 by 0.5 mm, apex rounded, glabrous; ovary c. 2 mm diam, densely hirsute, styles very short, stigmas deeply bifid, arms linear, 1–1.5 mm long, often curved. Fruits c. 1.3 cm diam, densely covered with fine hairs, smooth; wall 0.5–0.8 mm thick, exocarp detaching; columella 6–7 mm long. Seeds c. 6 mm diam; hilum triangular, c. 2.8 by 1.7 mm.

    Distribution — Sumatra (endemic).

   n (also including l) = T. magnificus; « = T. longipes; ▲= T. lychnos; l = T. malaccanus; ▼ = T. merrillii

    Habitat & Ecology — Recently logged-over or marshy forests. Flowering and fruiting: August.

    Note — A distinct but very rare species, known from two collections, the type and W.J.J.O. de Wilde & B.E.E. de Wilde-Duyfjes 19280, characterized by the tomentose indumentum, large and spreading inflorescences and sepals hairy on the inside.

18. Trigonostemon malaccanus Müll.Arg. (sect. Trigonostemon)

    Trigonostemon malaccanus Müll.Arg., Flora 47 (1864) 482; in A.DC., Prodr. 15, 2 (1866) 1110; Hook.f., Fl. Brit. India 5 (1887) 396; Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii (1911) 90; Ridl., Fl. Malay Penins. 3 (1924) 265; Jabl., Brittonia 15 (1963) 154; Whitmore, Fl. Malay Penins. 2 (1973) 136; Airy Shaw, Kew Bull. 36 (1981) 355; R.Y.Yu & Welzen, Blumea 62 (2018) 201, fig. 8, map 7; R.Y.Yu et al., Taxon 68 (2019) 928; R.Y.Yu & Welzen, Blumea 65 (2020) 38, map 11. — Type: K.D. Griffith 4782 (holo K), Malaya, Malacca.

    Trigonostemon laetus Baill. ex Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1109; Kurz, For. Fl. Burma 2 (1877) 407 (‘laetum’); Hook.f., Fl. Brit. India 5 (1887) 397; Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii (1911) 90. — Type: Wallich 7740 B (holo P), Malaya, Ambert.

Small trees, up to 6 m tall, stem at least up to 5 cm diam; flowering branches up to 7.5 mm thick, glabrous or slightly pubescent in young parts, sometimes hollow. Bark c. 0.3 mm thick, smooth, brownish to greyish to blackish; sap clear or orange; wood pale yellowish. Stipules falcate or subulate, c. 1 mm long, often pubescent near base. Leaves clustered near apex of branches; petiole terete but grooved above, 2.5–22 cm long, sometimes thickened at apex or base, slightly pubescent, glabrescent; blade lanceolate, oblong or occasionally ovate, 10–25(–40) by 3–14 cm, chartaceous to coriaceous, base acute to rounded, with 2 adaxial, subulate or falcate glands, margin distantly serrate, teeth small, falcate or nipple-like, apex acuminate to caudate, glabrous above, sparsely pubescent along venation beneath; midrib elevated and slightly pubescent (glabrescent in large leaves) on lower side, nerves 8–13 pairs, slightly curved and narrowed along margin, veinlets reticulate, often obscure. Inflorescences mainly unisexual, staminate ones thyrsoid, often terminal or subterminal, with short cymes along the main rachis, up to 25 cm long, densely hirsutellous, condensed when young; involucral bracts 2 or more, lanceolate to falcate, up to 2 by c. 0.5 mm; bracteate under cymes and under each flower, bracts lanceolate, up to 2 by 0.9 mm and 0.6 by 0.4 mm, respectively, hirsutulous; pistillate inflorescences racemose or thyrsoid, 1- or few-flowered cyme at each node, sometimes mixed with a few staminate flowers, up to 30 cm long, hirsutulous, condensed when young. Staminate flowers c. 4 mm diam; pedicel 1.5–2 mm long, 3–5 mm diam, hirsutulous; sepals orbicular to obovate, 1–2.1 by 0.6–1.6 mm, apex rounded, puberulent outside and often with a gland in the middle (on young flowers); petals obovate, c. 2.5 by 1.7 mm, pinkish or reddish purple, base cuneate, margin often wrinkled, apex rounded, glabrous on both sides; disc 0.6–1 mm diam, lobes obtrapezoid, c. 0.5 by 0.5 mm, c. 0.1 mm thick, glabrous, fused when young, separate and wrinkled when flowering, apex recurved and flat; stamens 3, androphore erect, c. 0.5 mm high, c. 0.2 mm diam, anthers free, long ellipsoid, c. 0.5 mm long. Pistillate flowers c. 4.5 mm diam; pedicel 1.5–2 mm long, 0.5–0.7 mm diam when flowering, slightly elongating to c. 4 mm long and 1 mm thick in fruit, hirsutulous; sepals and petals as staminate flowers, but petals caducous when fruiting; disc annular, margin irregularly undulate or with notches; ovary c. 1 mm diam, densely pubescent, style absent, stigmas deeply cleft for at least 3/4. Fruits c. 8 mm diam, puberulent, sepals persistent but not accrescent; wall 0.5–0.6 mm thick, exocarp detaching; columella 4.5–6 mm long. Seeds 5.5–6 by 5–5.5 mm; hilum triangular or heart-shaped, 2.5–3 by 2–2.5 mm.

    Distribution — Thailand, Malay Peninsula, Sumatra.

   l = T. malaccanus; « = T. longipes; ▲= T. lychnos; n (also including l) = T. magnificus; ▼ = T. merrillii

    Habitat & Ecology — Evergreen forests to recently logged-over forests on hill ridges or in valleys, sometimes near rivers. Altitude: 100–850 m. Flowering: all year round; fruiting: June to August, November to February.

    Vernacular name — Malay Peninsula: Putat.

    Notes — 1. Trigonostemon malaccanus resembles T. heteranthus but has stubby staminate pedicels (often shorter than 2 mm, wider than 0.3 mm diam) rather than the slim pedicels of T. heteranthus (often longer than 2 mm and c. 0.1 mm diam), and entire pistillate sepals (versus fimbriate in T. heteranthus).

    2. Trigonostemon malaccanus is also similar to T. verticillatus var. verticillatus but differs by having 5 instead of 3 stamens and the young inflorescences with distinct short and stiff hairs.

19. Trigonostemon merrillii Elmer (sect. Spinipollen)

    Trigonostemon merrillii Elmer, Leafl. Philipp. Bot. 4 (1911) 1304; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 407; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key, 44; R.Y.Yu & Welzen, Blumea 62 (2018) 203, map 7; R.Y.Yu et al., Taxon 68 (2019) 929; Blumea 65 (2020) 16, fig. 3, map 1. — Type: Elmer 12819 (holo PNH, †; iso BM, BO, L), Philippines, Palawan, Puerto Princesa (Mt. Pulgar).

Shrubs, 2–3 m tall, stem up to 2.5 cm diam; flowering branches terete, up to 5 mm diam. Indumentum densely sericeous, especially on young parts. Outer bark 0.1–0.2 mm thick, pale brownish, hairy; inner bark 0.2–0.3 mm thick, reddish black, with sap; sapwood c. 0.4 mm thick, reddish brown; heartwood c. 2 mm diam, pale yellowish or brownish; pith empty. Stipules lanceolate to linear, 1–3 mm long, sericeous, caducous. Leaves: petioles terete or often angled, 1–2.5 cm long, densely sericeous; blade elliptic, 10–24 by 5–9.5 cm, chartaceous, base rounded or cordate, 2 adaxial glands present but often covered by silky hairs, margin distantly serrate, teeth often apiculate, falcate when young, apex acute to acuminate to caudate, upper surface greenish, paler beneath, both sides covered by long silky hairs; midrib slightly raised above and much elevated beneath, more densely sericeous, nerves 10–13 pairs, curved and connected near margin, veins and veinlets reticulate, sometimes obscure. Inflorescences: staminate ones thyrsoid with glomerulus along the main rachis, peduncle slender, 8–9 cm long and 0.4–0.7 mm diam, sericeous, with a few depauperate glomerulus below; involucral bracts subulate, at the base of inflorescences, c. 1.2 mm long, base hairy, bracts lanceolate, under each node, 1.1–3 mm long, sericeous; pistillate inflorescences racemose, main rachis slender, up to 12 cm long, c. 0.6 mm diam, sericeous; bracts as in staminate inflorescences. Staminate flowers 2.8–3.5 mm diam; pedicels c. 1 mm long, 0.15 mm diam, glabrescent; sepals unequal, elliptic to spathulate, 0.9–1.3 by 0.7–0.8 mm, narrowed near base, margin entire or slightly undulate, acute to rounded at apex, more or less pubescent outside; petals spathulate, 1.3–2.2 by 1.2–1.6 mm, dark purple, base cuneate, apex rounded, glabrous on both sides; disc cupular, slightly wrinkled, 5-toothed, each tooth rectangular, c. 0.2 by 0.2 mm, apex truncate, glabrous; stamens 3, androphore erect, 0.4–0.5 mm high, anthers ellipsoid, 0.25–0.35 mm long, gathered on the top of androphore, slightly divaricate at apex, connectives apically with some droplets (expanded cells) with secretion. Pistillate flowers unseen. Fruits c. 1.25 cm diam, glabrous; sepals not much accrescent. Seeds streaked or conspicuously mottled.

    Distribution — Philippines (endemic).

   ▼ = T. merrillii; « = T. longipes; ▲= T. lychnos; n (also including l) = T. magnificus; l = T. malaccanus

    p = T. merrillii; l = T. filiformis; n = T. palustris; « = T. victoriae

    Habitat & Ecology — Lowland dipterocarp forest. Altitude: 15 m. Flowering: March.

    Note — The species resembles T. oblongifolius in the staminate inflorescences but differs from the latter by the blade being hairy on both sides. The description of fruits is based on Elmer (1911).

20. Trigonostemon oblongifolius Merr. (sect. Spinipollen)

    Trigonostemon oblongifolius Merr., Philipp. J. Sci. 7, Bot. (1912) 409; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 407; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.Y.Yu & Welzen, Blumea 62 (2018) 203, map 8; R.Y.Yu et al., Taxon 68 (2019) 929. — Type: BS (Ramos) 13965 (holo PNH, †; iso A, US), Philippines, Luzon, Prov. Cagayan, Abulug River.

    Trigonostemon luzoniensis Merr., Philipp. J. Sci. 16 (1920) 568; Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47. — Type: PNH (Ramos & Edaño) 33539 (holo PNH, †; iso K), Philippines, Luzon, Camarines Prov., Paracale.

Small trees, up to 6 m tall; flowering branches terete, 2–4.5 mm diam, whitish and sparsely pubescent when young, buds densely golden pubescent. Bark c. 0.2 mm thick, smooth, pale brownish. Stipules subulate or falcate, 0.5–1 mm long, caducous, pubescent near base. Leaves: petiole terete but often grooved above, 0.5–3.5 cm long, more or less hirsute; blade oblong, 4–23 by 2–6.5 cm, coriaceous, base acute or rounded, margin often slightly recurved, apex acute, upper side paler (when dry), glabrous above and sparsely pubescent beneath; midrib often elevated and hirsute beneath, nerves 6–12 pairs, curved and often connected along margin, veinlets almost indistinct. Inflorescences: staminate ones (pre-flowered) paniculate thyrses, often axillary, at most few branched and with short glomerate cymes along the main rachis and the lateral branches, main rachis up to 18 cm long, 0.5–1 mm thick, slightly pubescent, bracteate under each branch, bracts lanceolate, c. 2 by 0.6 mm, hirsute outside; secondary branches often short, 0.5–1.5 cm long, cymes scorpioids, clustered, paintbrush- or broom-like, few-flowered, each flower bracteate; the latter lanceolate, up to 0.8 by 0.5 mm, hairy outside; pistillate ones (post-flowered, infructescences) racemose, axillary, c. 5 cm long, glabrescent; bracts lanceolate, c. 1.5 by 0.7 mm, glabrous. Staminate flowers (unopened) c.1.5 mm diam; pedicel c. 1 mm long, glabrous; sepals orbicular to ovate, c. 1.4 by 1.3 mm, imbricate, slightly hairy outside; petals ovate, c. 0.5 by 0.5 mm, glabrous; disc indistinct; stamens 3, androphore short, hidden, anthers gathered into a head on the top of androphore, c. 0.3 mm long. Pistillate flowers (fruiting): pedicel 2–2.2 cm long, thickened towards apex and scarcely hairy, sepals elliptic, c. 1.2 by 0.8 mm, outside sparsely pubescent near base; ovary villous; stigmas apically cleft, the lobes c. 0.5 mm long. Fruits c. 1 cm diam, appressed hirsute, warty; wall c. 0.6 mm thick, exocarp partly splitting off; columella c. 5.5 mm long. Seeds c. 6 by 6.5 mm, dark brown; hilum heart-shaped, 2.5–3 by 1.5–1.8 mm.

    Distribution — Philippines (Luzon, endemic).

    ▼ = T. oblongifolius; ▲ = T. pentandrus; n = T. polyanthus; l = T. rufescens; « = T. sandakanensis

    Habitat & Ecology — Flowering: January.

    Note — The description of the ovary is based on Merrill (1912). The species has similar-looking inflorescences as T. polyanthus, but the main rachis is more distinct and the secondary rachis is much shorter and condensed than those of the latter species.

21. Trigonostemon palustris R.Y.Yu & Welzen  (sect. Trigonostemon)

    Tigonostemon palustris R.Y.Yu & Welzen in R.Y.Yu et al., Blumea 65 (2020) 20, fig. 4, 5, map 1.  — Type: Yu 260 (holo PNH; iso DLSUH, L), Philippines, Palawan Province, El Nido, trail to the Nakalit-kalit Waterfalls.

Small trees, c. 2 m tall; flowering branches terete, 3–3.7 mm diam., pubescent in young parts. Outer bark grey, 0.1–0.2 mm thick; inner bark 0.1–0.2 mm thick, red, sap red; wood pale yellow. Stipules subulate or falcate, 0.7–1.4 mm long, caducous, base pubescent. Leaves: petioles terete, slightly thickening towards both ends, 3–7 cm long, 1.6–2 (middle part)–3 mm (apex or base) diam, glabrescent; blade elliptic, 12–23 by 5.5 –7.7 cm, chartaceous to coriaceous, base acute, 1– 2 pairs of adaxial glands present, margin distantly serrate, teeth subulate, apex acuminate to caudate, upper side (somewhat dark) green, glabrous, lower side pale green, often slightly pubescent, particularly on venation; midrib flat or very slightly grooved above, elevated beneath, nerves 8–11 pairs, curved and connected near margin, veins and veinlets reticulate. Inflorescences bisexual or unisexual, terminal or axillary, racemose thyrses; main rachis 2–4.5 cm long, 0.6–1.2 mm diam, densely pubescent, few (up to 10) staminate flowers clustered per node, pistillate flowers single per node; involucral bracts as stipules; bracts triangular, 0.7–2.6 by 0.5–0.7 mm, pubescent on both sides. Staminate flowers 5–7 mm diam; pedicel 1.5–2 mm long, 0.3–0.4 mm diam, green, slightly pubescent; sepals orbicular to elliptic, 0.8–1.3 by 0.4–0.9 mm, light green, base connate, margin entire, apex rounded to acute, pubescent outside, glabrous inside; petals flabellate, 1.5–1.9 by 1.4–1.6 mm, yellow, base cuneate, margin entire, apex slightly bilobed, glabrous on both sides; disc annular, c. 0.2 mm diam (inner margin), c. 0.2 mm thick, yellow; stamens 3, androphore erect, 0.4–0.5 mm long, anthers ellipsoid, 0.3–0.4 mm long, divaricate at apex. Pistillate flowers 4–6 mm diam; pedicel 3.5–5 mm long, thickening towards the apex, 0.6–0.9 mm diam (apex), light greenish to pinkish, pubescent; sepals elliptic, 5–7 by 2–3.5 mm, pink, base connate, margin serrate, apex acuminate, with 3 main teeth; petals obovate to spathulate, 3.4–4.2 by 2.5–3.4 mm, yellow, base cuneate, apex rounded, sometimes slightly plicate, glabrous on both sides; disc annular, 2.2–2.6 diam, c. 0.1 mm thick; ovary 1.9–2 mm diam, glabrous, style 0.1–0.2 mm long, stigmas completely bifid, arms 0.7–1 mm long. Fruits light green, glabrous; sepals persistent, not much accrescent, green, stigmas persistent, pinkish.

    Distribution  — Philippines (Palawan, endemic).

    n = T. palustris; l = T. filiformis; p = T. merrillii; « = T. victoriae

    Habitat & Ecology — Lowland forest edge, in swamps (hence the specific epithet). Altitude: c. 25 m. Flowering: February, April; fruiting: February.

    Note — This new species was first brought to our attention by images published on Co’s Digital Flora of the Philippines (www.philippineplants.org), and we are grateful to the owners of the photos who gave us permission to re-use them in this article. The species has two relatively unusual characters: pistillate sepals being larger than petals and yellow petals in both staminate and pistillate flowers. It is the only species with yellow petals in sect. Trigonostemon. These characters are only known to occur separately in a few species, e.g., T. victoriae (larger sepals than petals in pistillate flowers), and T. laevigatus and T. philippinensis (yellow petals), but they are all clearly different from this new species. The species is found to cohabit with ants (Fig. 4i; Yu pers. obs.).

22. Trigonostemon pentandrus Pax & K.Hoffm. (sect. Trigonostemon)

    Trigonostemon pentandrus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 406; Jabl., Brittonia 15 (1963) 164; R.Y.Yu & Welzen, Blumea 62 (2018) 204, fig. 9, 10, map 8; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: Hubert Winkler 1792 (?), Malaya, Gunung Angsi near Sungei Gadub. Epitype (designated here): KEP FRI (R.Y. Yu) 86653 (holo L; iso KEP), Malaysia, Negri Sembilan, Gunung Angsi.

Small trees, 1–2.5 m tall; flowering branches 5–7 mm diam, pith sometimes of loose tissue. Outer bark 0.2–0.25 mm thick, pale greyish, slightly fissured, glabrous; inner bark 0.15–0.4 mm thick, dark reddish to brownish, fibrous, sap orange; wood 0.5–0.6 mm diam, whitish to yellowish. Stipules subulate to nipple-like, 0.5–1 mm long, glabrous. Leaves: petiole terete, 3.5–8 cm long, 2–3.2 mm diam, glabrous, thickened at base and apex, base somewhat sheathing; blade oblong, 23–35 by 6–9.5 cm, coriaceous, base cuneate, with 2 adaxial glands, nipple-like, showy, margin distantly serrate, teeth short-subulate, thickened, apex acuminate to caudate, upper side dark green, lower side pale green, both sides glabrous; venation penninerved, glabrous, midrib robust, slightly raised above and distinctly elevated beneath, nerves 14–16 pairs, straight, narrowed and branched and connected along margin, veinlets reticulate, often obscure. Inflorescences bisexual, (sub)terminal, short racemose, rigid, staminate flowers at top, pistillate flowers below, 2–6.5 cm long, rachis 1.3–2 mm diam, densely hirsutulous. Staminate flowers 6–7 mm diam; pedicel 2–3 mm long, 0.4–0.5 mm diam, pinkish red, hispidulous; sepals elliptic, 1.3–2 by 1–1.5 mm, white, base connate, margin entire or slightly irregularly undulate, ciliate, apex acute to rounded to emarginate, hirsutulous outside, glabrous inside; petals obovate, 3–4.2 by 2.5–3.2 mm, pink, base narrowed and somewhat claw-like, margin often wrinkled, apex bilobed, glabrous on both sides; disc lobes glandular, 0.6–0.7 by 0.3–0.6 mm, c. 0.15 mm thick, glabrous; stamens 5, androphore erect, 0.7–1 mm long, 0.2–0.3 mm diam near base, slightly narrowed above, 5-cleft at apex; anthers ellipsoid, 0.9–1 mm long, free, divaricate, connectives apically often with numerous dark reddish droplets (expanded cells) with secretion. Pistillate flowers c. 0.3 mm diam (petals fallen); pedicel c. 1.7 mm long, articulated at base, c. 0.5 mm diam when flowering, slightly elongating in fruit to 3.5–4.5 mm long and c. 1.5 mm diam, hirsutulous; sepals elliptic to triangular, 2–2.8 by 1–1.2 mm, margin entire, ciliate, apex rounded to acute to acuminate, hirsutulous outside, glabrous inside; petals not seen, fallen; disc as staminate flowers; ovary c. 1.2 mm diam, reddish, densely hispid; styles indistinct; stigmas deeply fibid into 2 arms of 1.2–1.5 mm length, thickened at apex. Fruits c. 5.5 mm diam, red in living plants, brownish when dry, densely hispid, sepals (slightly accrescent) and stigmas persistent; wall 0.4–0.5 mm thick, exocarp less than 0.1 mm thick, not detaching; columella c. 5 mm long. Seeds not seen.

    Distribution — Malay Peninsula (Gunung Angsi, endemic).

    ▲ = T. pentandrus; ▼ = T. oblongifolius; n = T. polyanthus; l = T. rufescens; « = T. sandakanensis

    Habitat & Ecology — Flowering and fruiting: September to December.

    Notes — 1. The species resembles T. verticillatus but a few unusual or unique characters make the species quite distinct: thicker leaves, one pair of showy blackish adaxial glands on leaves (glands not showy, but sometimes can be two pairs in T. verticillatus), shorter inflorescences and pinkish instead of reddish purple flowers.

    2. The species has remained inadequately known and was only mentioned once (Jablonski 1963) since the original publication. The original type collection (Hubert Winkler 1792) is not seen by us and is presumably lost, but our field observations and collections from Gunung Angsi (type locality) match the original description by Pax & Hoffman (1914) very well. We are strongly convinced that this is a good and distinct species. For more specimen citations, see Identification List in Yu & Welzen (2018).

23. Trigonostemon philippinensis Stapf (sect. Tylosepalum)

        Trigonostemon philippinensis Stapf, Leafl. Philipp. Bot. 1 (1907) 206; Pax & K.Hoffm. in Engl., Pflanzenfam. IV.147.iii (1911) 91; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Kew Bull. 36 (1981) 355; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 29, in key; R.Y.Yu & Welzen, Blumea 62 (2018) 206, fig. 11, map 9; R.Y.Yu et al., Taxon 68 (2019) 930; R.Y.Yu & Welzen, Blumea 65 (2020) 41, map 12. — Type: Elmer 8326 (holo PNH, †; iso BO, K, L), Philippines, Luzon, Laguna Prov., Los Baños.

    Trigonostemon thrysoideus Stapf, Bull. Misc. Inform. Kew (1909) 264 (‘thyrsoideum’); Airy Shaw, Kew Bull. 26 (1972) 348; H.S.Kiu, Fl. Reipubl. Popul. Sin. 44(2) (1996) 166; Chantar., Thai Forest Bull. (Bot.) 33 (2005) 29; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 584, plate 32: 1; P.T.Li & M.G.Gilbert. in C.Y.Wu, P.H.Raven & D.Y.Hong, Fl. China 11 (2008) 274. — Type: A. Henry 11947 (A, K, NY), China, Yunnan, Simao (Szemao).

    [Trigonostemon paniculatus Merr. ined., refered to by Jabl., Brittonia 15 (1963) 163 (as a synonym of T. sumatranus Pax & K.Hoffm.)].

Trees or treelets, 6–15(–20) m tall, dbh 6–25(–40) cm, flowering branches up to 6.5 mm thick, brownish, glabrescent, slightly scaberulous basally. Outer bark hard, 0.5–1 mm thick, brownish to greyish, rugose, lenticellate; inner bark 2–5 mm thick, pinkish to reddish, brownish (when dry); exudate clear, pinkish; wood dirty pinkish white. Stipules falcate, sometimes linear, up to 1.5–2 by c. 0.4 mm, pubescent near base, caducous. Leaves: petiole terete, 1.5–15 cm long, 0.8–2.5 mm diam, glabrous or slightly pubescent, base in apical leaves often somewhat sheathing; blade elliptic to sometimes obovate, 10–31 by 4–13.5 cm, coriaceous, base acute or cuneate, with 2 adaxial falcate glands, margin distantly serrate to crenate, teeth subulate or falcate, apex acuminate to caudate, sometimes acute, dark green above, pale green beneath, both sides glabrous or with a few very scattered hairs; venation often slightly pubescent, midrib slightly raised above and raised beneath, nerves 8–14 pairs, curved, branched and connected along margin, veins and veinlets reticulate, obscure. Inflorescences often terminal, paniculate, much branched and many-flowered, up to 30 cm long (up to 15 cm long in the Philippines), usually unisexual to bisexual, finely pubescent; bracteate under each node, bracts triangular, 0.5–2.5(–5) by 0.2–1 mm (larger ones basal in inflorescence, smaller ones higher up; often longer in Thai and Vietnamese specimens), outside pubescent, inside glabrous, on large branches sometimes caducous and often with 2 falcate or subulate bracteoles at the sides (Sumatra and Borneo), up to 1 mm long. Staminate flowers c. 5 mm diam; pedicel 3.5–4 mm long, c. 0.2 mm thick, pubescent, articulate at base; sepals elliptic or somewhat obovate, 1.2–1.6 by 0.6–0.8 mm, pale greenish or greenish yellow, base narrowed and connate, margin somewhat translucent, apex rounded or slightly undulate, outside pubescent, often with a gland in the middle, inside glabrous; petals obovate to spathulate, 2.5–4 by 1.2–2 mm, base cuneate to claw-like, entire, apex rounded, yellowish, sometime pale cream inside and with a paler margin (Philippines), midrib and few parallel veins visible, glabrous; disc lobes trapezoid, 0.2–0.3 by 0.2–0.3 mm, c. 0.1 mm thick, fleshy, apex thickened, reflexed; stamens 3, androphore c. 0.5 mm long, free terminal part sometimes slightly trifid at top, sometimes bent (Sumatra and Borneo), anthers splitting off subapically from androphore, ellipsoid, c. 0.2 mm long, cream, divaricate (mainly in specimens from Thailand and Vietnam), connectives apically with droplets with secretion. Pistillate flowers of same size as staminate ones; pedicel 2.5–3.5 mm long, apex slightly thickened, 0.6–0.7 mm thick; sepals and petals as in staminate flowers; disc lobes rectangular, c. 0.4 by 0.6 mm, apex truncate; ovary c. 1 mm diam, glabrous and warty, styles extremely short, stigmas with a shallow groove above. Infructescence pendulous, dull pale light green. Fruits c. 1.5 cm diam, greenish, glabrous, warty or aculeate above; pedicel 2.5–4 cm long, green; sepals persistent but not accrescent; wall woody, c. 0.6 mm thick, exocarp partly detaching; columella c. 0.8 cm long. Seeds 6–7.5 mm diam, dark brown when dry; hilum long-triangular to heart-shaped, 1–2.5 by 0.5–1.2 mm.

    Distribution — Thailand, Vietnam, Malay Peninsula, Sumatra, Borneo, Philippines.

    Habitat & Ecology — Lowland evergreen to deciduous forests, sometimes on limestone hills, near rivers; growing on red to yellow calcareous soils to granite bedrocks. Flowering and fruiting: all year round.

   Notes — 1. The inflorescences are mainly unisexual because they generally consist of flowers of the same gender but sometimes are mixed with a few flowers of the other sex. The flowers can spread evenly along secondary rachis, whereby the whole panicle attains a pyramid-shape (Thailand and Vietnam), or the flowers cluster in brush- or broom-like groups on tertiary branches and the inflorescences seem more umbellate (Sumatra and Borneo).

    2. Many collections (in many herbaria) of this species are incorrectly identified either as T. sumatranus or T. paniculatus (or ‘T. paniculatum’) for a historical reason.

Pax & Hoffman’s (1911) T. sumatranus was based on Forbes 2647 (BM, K, L), and is actually a synonym of T. viridissimus, a species that also bears paniculate inflorescences but can be easily distinguished from T. philippinensis by its much shorter petioles and stigmas being almost not bifid.

Merrill’s T. paniculatus (‘paniculatum’) ined. was based on rich collections, which are actually T. philippinensis, but he never published this name, because he thought T. paniculatus could be the same as T. sumatranus (Jablonski 1963).

Jablonski (1963) never saw Forbes 2647 and he misbelieved that T. sumatranus and T. paniculatus were conspecific, and therefore connected these two misperceptions, which explains these common misidentifications accordingly.

24. Trigonostemon polyanthus Merr. (sect. Trigonostemon)

    Trigonostemon polyanthus Merr., Philipp. J. Sci. 9, Bot. (1914) 492; Enum. Philipp. Fl. Pl. 2 (1923) 452; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 48; R.Y.Yu & Welzen, Blumea 62 (2018) 207, map 8; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: BS (Ramos) 1645 (holo PNH, †; iso BM, BO, L, SING), Philippines, Samar, Cauayan Valley.

    Trigonostemon diffusus Merr. subsp. condensus R.I.Milne, Kew Bull. 50 (1995) 47; R.Y.Yu & Welzen, Blumea 62 (2018) 207, map 8. — Type: PNH (Lagrimas et al.) 39433 (holo K; iso L, PNH, †), Philippines, Luzon, Camarines Norte Province, Ilyang Binuauangan.

Shrubs, 2–3 m tall; flowering branches terete, 1.5–3 mm diam, slightly pubescent when young. Outer bark c. 0.1 mm thick, pale greyish, smooth; inner bark c. 0.1 mm thick, reddish brown; wood pale red or yellow. Stipules subulate or falcate, 0.5–1 mm long, pubescent. Leaves: petiole 0.8–3.2 cm long, pubescent, sometimes thickened at apex and base; blade elliptic, 4–15 by 2–4.5 cm, membranous or chartaceous, base truncate to rounded to acute, often with 2 adaxial falcate glands, margin entire or slightly distantly serrate, apex acuminate, upper surface glabrous, lower surface glabrescent to scattered pubescent; venation penninerved, slightly pubescent on lower side, midrib slightly raised above and elevated beneath, nerves 5–9 pairs, bow-shaped, connected along margin, veins and veinlets reticulate, often obscure. Inflorescences axillary, staminate ones paniculate thyrses, pubescent, main rachis up to 10 cm long, along secondary rachises (or tertiary rachises) scorpioid cymes, paintbrush-like and many-flowered, bracts linear to triangular, 0.5–5 by 0.2–0.5 mm, pubescent outside; pistillate inflorescences cymose, 1- or few-flowered near apex and with few depauperate flowers below, peduncles c. 3 cm long, pubescent, bracts as staminate ones. Staminate flowers c. 4 mm diam; pedicel 2.5–3.5 mm long, c. 0.2 mm thick, pubescent; sepals elliptic, 1.2–1.6 by 0.3–0.6 mm, pubescent outside, margin sometimes slightly ciliate, apex acute to rounded; petals obovate to spathulate, 2.5–3 by 1–1.3 mm, base cuneate, margin entire, apex rounded, dark purplish and with one yellow or red flame-like honey mark in the lower middle part, glabrous, smooth; disc lobes oblong to trapezoid, c. 0.3 by 0.2 mm, c. 0.1 mm thick, apex acute or obtuse, glabrous; stamens 3, androphore erect, c. 0.5 mm long, anthers clustered at top of androphore, ellipsoid, c. 0.5 mm long, connectives apically with numerous droplets (or expanded cells) with secretion. Pistillate flowers c. 5.5 mm diam; pedicel slightly thickened towards apex, c. 4 mm long, apically c. 0.7 mm diam, sericeous; sepals oblong or lanceolate, 3.5–4.5 by 1–1.2 mm, margin sometimes with a few teeth, apex acute to acuminate, sericeous outside, often sparsely sericeous inside; petals as staminate flowers but larger, 4–4.5 by 1.5–2.7 mm; disc lobes semi-orbicular, c. 0.5 by 0.5 mm, apex rounded to acute; ovary c. 0.9 mm diam, densely pubescent, styles indistinct, stigmas c. 0.7 mm long, deeply bifid into 2 arms, each arm c. 0.55 mm long, thickened abaxially, base horseshoe-shaped. Fruits and seeds not seen.

    Distribution — Philippines (Samar and Luzon).

    n = T. polyanthus; ▼ = T. oblongifolius; ▲ = T. pentandrus; l = T. rufescens; « = T. sandakanensis

    Habitat & Ecology — Flowering: April to June.

    Notes — 1. A distinct species with paintbrush-like staminate inflorescences. Only 2 specimens present, the type specimen from Samar and PHN (M. Lagrimas et al.) 39433 from Luzon.

    2. Milne (1995) wrongly cited PNH (Ramos) 42686 as type of T. polyanthus (but later corrected this in an erratum via a printed sheet among the specimens), as it is not the type and actually belongs to T. villosus. Therefore, the reference of Milne (1995) is not listed under T. polyanthus.

    3. The holotype for T. diffusus subsp. condensus cited by Milne (1995), PHN (M. Lagrimas et al.) 39437, might be a misprint as it should be PHN (M. Lagrimas et al.) 39433 (same date and place as 39437). He also cited BS (Ramos) 1645 as a paratype, but he probably did not notice that it was the type of an older name – T. polyanthus. Although T. diffusus shares some similarity with T. polyanthus in the inflorescences, the differences are also striking and necessitate that both species are kept distinct, e.g., the inflorescences of T. diffusus are more elongated, diffuse and paniculate with a relative clear main rachis in the middle (PNH (M. Lagrimas et al.) 56725) and much longer internodes, and the pedicels are glabrous and thinner. Both species are relatively rare, more collections are desired.

25. Trigonostemon rufescens Jabl. (sect. Trigonostemon)

    Trigonostemon rufescens Jabl., Brittonia 15 (1963) 152, fig. 2; Whitmore, Tree Fl. Malaya 2 (1973) 135; R.Y.Yu & Welzen, Blumea 62 (2018) 209, fig. 12, map 8; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: SFN (Corner) 29428 (holo SING; iso BO, K, L, SAN, SING), Malaysia, Johore, 13.5 miles on Mawai – Jemaluang Road.

Small trees, up to 3 m tall; flowering branches 4–6 mm diam. Indumentum of densely golden hispid hairs. Outer bark c. 0.1 mm thick, dark brownish, hispid; inner bark c. 0.1 mm thick, blackish, sap red; sapwood 0.85–1 mm thick, whitish to pale yellowish; heartwood 2.6–2.8 mm diam, pale brownish, often hollow. Stipules subulate, c. 1 mm long, densely hispid, caducous. Leaves: petiole subterete, more or less furrowed above, 2–13 cm long, hispid; blade oblong to oblanceolate, 18–32 by 5–12 cm, coriaceous, base cuneate, acute to rounded or narrowly cordate, 2 adaxial glands often present, margin very distantly serrate, teeth subulate, apex acuminate to aristate, densely golden hispid on both sides; midrib flat above and elevated beneath, with two layers of hairs, soft pilose and hispid, nerves 11–14 pairs, curved and narrowed near margin, veins reticulate, often obscure above and distinct beneath. Inflorescences: staminate ones racemes or glomerules, 2–9 cm long, hispid; bracts lanceolate or linear, 8–20 by 1–5 mm, hispid; pistillate inflorescences racemose, up to 6 cm long, axillary, few-flowered (often only the top one develops), hispid; bracts as staminate ones. Staminate flowers c. 6 mm diam; pedicel at least 3.5 mm long, c. 0.4 mm diam, sparsely hirsutulous; sepals oblong, at least 3 by 1.2 mm, villose outside, glabrous inside; petals obovate or oblong, 3.5–5.5 by 1.5–2.2 mm, dark reddish, both sides glabrous; disc lobes elliptic, c. 0.4 by 0.4 mm, apex acute, glabrous; stamens 5, androphore erect, c. 1.5 mm long, 5-cleft at top, filament 0.3–0.4 mm long, anthers free, divaricate at top into two lobes, each lobe 0.65–0.8 mm long. Pistillate flowers c. 1.2 cm diam; pedicel c. 6.5 mm long, c. 0.7 mm diam, hispid; sepals lanceolate, 5.5–6.6 by 1.5–2.5 mm, apex acuminate, densely hispid outside, sparsely hispid inside; petals elliptic, c. 4.5 by 2 mm, margin wrinkled and irregular, apex near acute, glabrous on both sides; disc lobes rectangular to semi-orbicular, c. 0.4 by 0.8 mm, glabrous; ovary c. 1.3 mm diam, glabrous, evenly narrowed at top, styles c. 0.3 mm long, stigmas c. 1 mm long, bifid to middle. Fruits (immature) c. 7 mm diam, pinkish, pedicel c. 1 cm long, c. 2 mm diam (top); persistent sepals triangular, 1.2–1.5 by 0.6 mm. Seeds not seen.

    Distribution — Malay Peninsula (Mawai – Jemaluang Road, endemic).

    l = T. rufescens; ▼ = T. oblongifolius; ▲ = T. pentandrus; n = T. polyanthus; « = T. sandakanensis

    Habitat & Ecology — In drier part of swamps and on dry hill rocks. Flowering: February, May.

    Notes — 1. This is a densely hairy species but the ovary turns out to be completely glabrous in our dissection, which is different from Jablonski’s (1963) original description.

    2. It is only known from its type locality where most of the forests have been replaced by oil palm plantations and the species, resampled in 2016 by the first author, is now extremely threatened.

26. Trigonostemon sandakanensis Jabl. (sect. Spinipollen)

    Trigonostemon sandakanensis Jabl., Brittonia 15 (1963) 159, figs. 5, 6; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 204; R.I.Milne, Kew Bull. 50 (1995) 27, in key, 30, in key; R.Y.Yu & Welzen, Blumea 62 (2018) 209, fig. 13, map 8; R.Y.Yu et al., Taxon 68 (2019) 929. — Type: SAN (Wood) 16018 (holo SING; iso BO, BRI, K, KEP, L, SAN, SING), British North Borneo [Sabah], Kabili-Sepilok Forest Reserve, 15 miles W of Sandakan, Compartment 10.

Small trees, up to 5 m tall; barely branching, main branch occasionally with adventitious roots; flowering branches c. 1.2 cm diam. Outer bark dark brownish, slightly wrinkled; inner bark brown, sap red; sapwood pale yellowish; heartwood white. Stipules not seen, caducous, scars 0.5–0.6 mm diam. Leaves clustered at the end of branchlets; petiole less than 1 cm long, often lignified and somewhat sheathing; blade oblanceolate, large, 35–45 by 9–13 cm, coriaceous, base cuneate, evenly narrowing into the petiole, margin distantly serrate, teeth subulate, apex caudate, acuminate, apiculate or notched, dark green above, dull and pale green beneath, both sides sericeous; midrib slightly raised on both sides, robust, pubescent and velutinous, nerves 30–40 pairs, curved and more or less connected near margin, veins scalariform, veinlets reticulate, often obscure. Inflorescences: staminate ones subterminal, thyrsoid, short cymes on each node, main rachis erect, up to 20 cm long, sericeous; bracts linear or narrowed lanceolate, up to 7.5 by 1 mm, apex acuminate, abaxially sericeous; pistillate inflorescences racemose, almost spike-like when young, c. 5 cm long when flowering, up to 20 cm long when fruiting, densely sericeous. Staminate flowers 6–10 mm diam; pedicel 5–8 mm long, c. 0.2 mm diam, slightly hairy; sepals elliptic, 2–3 by 1.5–2 mm, apex rounded, reddish, glabrous on both sides; petals linear, 8–9 by 1.2–1.6 mm, margin often reflexed, apex acute, pinkish or pale purplish, outside smooth, inside rough, somewhat papillate and with numerous small and short, generally longitudinal ridges; disc annular, c. 1.6 mm diam, c. 0.4 mm wide, fence-like because of c. 20, apically undulate lobes; stamens 5, androphore erect, 0.6–1 mm long, pubescent at base, anthers clustered at top of androphore, ellipsoid, c. 0.7 mm long, thecae orange and connectives blackish when dry, thickened, protruding and often with few expanded cells apically. Pistillate flowers of same size as staminate ones; pedicel c. 7 mm long, apically c. 0.8 mm diam, elongating in fruit to up to 4 cm long, apically c. 1.5 mm diam, densely sericeous; sepals, petals and disc as staminate flowers; ovary c. 1 mm diam, densely sericeous, style c. 0.2 mm long, stigmas c. 0.7 mm long, bifid into 2 slightly thickened arms, each arm c. 0.5 mm long. Fruits c. 1 cm diam, hirsute, sepals persistent but not accrescent; wall c. 0.7 mm thick, exocarp partly detaching; columella 5–6.5 mm long. Seeds 7–7.5 mm diam; hilum rhombic, 3–4 by 2.5–3.5 mm.

    Distribution — Borneo (Sabah, endemic).

    « = T. sandakanensis; ▼ = T. oblongifolius; ▲ = T. pentandrus; n = T. polyanthus; l = T. rufescens

    Habitat & Ecology — Primary forest, near stream. Altitude: 5–20 m. Flowering: April to June; fruiting: December.

    Note — A unique species only known from the Kabili-Sepilok Forest Reserve in Sandakan, Sabah. The petals are linear and the inner surface is very rough and scurfy.

27. Trigonostemon scopulatus R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon scopulatus R.Y.Yu & Welzen, Blumea 62 (2018) 210, fig. 14, map 10; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: KEP FRI (P.F. Cockburn) 7859 (holo L, iso K, KEP, SING), Malaysia, Johore, Ulu Endau. Labis FR. Compt. 277.

Small trees, up to 3 m tall; flowering branches c. 3.5 mm diam, sometimes hollow. Outer bark 0.1–0.2 mm thick, dark brownish, tomentellous; inner bark 0.1–0.3 mm thick, dark reddish to blackish; sapwood 1.5–2 mm thick, brown; heartwood c. 1.5 mm diam, brown. Stipules subulate, c. 0.5 mm long, often covered with hairs. Leaves: petiole terete, 2.5–12 cm long, hispidulous; blade oblong, 12–26 by 4–7.5 cm, chartaceous, base narrowly cordate, glands not seen, margin entire or slightly, distantly serrate, apex acuminate, upper side dark brownish to black (when dry), glabrous, lower side brown (when dry), papillate-hispid; venation penninerved, papillose hispid on lower side, midrib flat above and elevated beneath, nerves 10–13 pairs, straight or slightly curved, branched and connected along margin, veins scalariform, veinlets reticulate. Inflorescences bisexual, in the leafless parts fascicled, in the axils of still present leaves elongated and racemose or thyrsoid, with the flowers concentrated at the upper part of the rachis and broom-like, rachis up to 10 cm long, 0.8–1 mm diam, densely hispid; bracts lanceolate, 4–5 by 0.6–1.2 mm, apex acuminate, densely hispid outside, glabrous inside. Staminate flowers 2.5–3.5 mm diam; pedicel 4.5–5.5 mm long, 0.2–0.3 mm diam, hispidulous; sepals lanceolate to linear, 1–1.5 by 0.2–0.3 mm, margin entire or slightly serrate, apex acuminate, outer surface hispid and with few whitish oil-like spots; petals elliptic, 1.2–1.5 by 0.7–0.8 mm, dark red to purple, glabrous on both sides; disc lobes rectangular to obtrapezoid, c. 0.2 by 0.2 mm, apex truncate, often slightly revolute; stamens 3, androphore c. 0.4 mm long; anthers gathered on the top of androphore, ellipsoid, c. 0.5 mm long. Pistillate flowers 0.45–0.5 mm diam; pedicel 6–8 mm long, 0.4–0.5 mm diam, densely hispid; sepals lanceolate, 2.5–3 by c. 0.5 mm, margin entire, apex acuminate, hispid outside, glabrous inside; petals elliptic, 2.4–3 by 1–1.5 mm, dark red, margin entire, base and apex acute, glabrous outside, rough and slightly papillate inside; disc obtrapezoid, c. 0.45 by 0.45 mm, apex truncate; ovary c. 0.8 mm diam, glabrous; styles short, sometimes indistinct, c. 0.1 mm long; stigmas deeply bifid, arms 0.6–0.7 mm long, bent, thickened abaxially and sagittate near base. Fruits and seeds unknown.

    Distribution — Malay Peninsula (endemic, only found in Johor, Malaysia and Singapore).

   u = T. scopulatus; ▼ = T. serratus; l = T. sinclairii; n = T. victoriae; « = T. wetriifolius; ▲ = T. wildeorum

    Habitat & Ecology — Disturbed forest near logging road; moist gully. Altitude: low. Flowering: March.

28. Trigonostemon serratus Blume (sect. Trigonostemon)

    Trigonostemon serratus Blume, Bijdr. (1825) 600 (‘serratum’); Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1110; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 92; Backer & Bakh.f., Fl. Java 1 (1963) 495; Airy Shaw, Kew Bull. 37 (1982) 36; R.Y.Yu & Welzen, Blumea 62 (2018) 212, map 10; R.Y.Yu et al., Taxon 68 (2019) 929. — Lectotype (designated by Yu & Welzen 2018): Blume 1648 (L, barcode L.2258717; iso L, barcodes L.2258713, L.2258714, L.2258716), Java, Nusa Kambanga.

Small trees; flowering branches terete, 2–3 mm diam, buds densely sericeous. Outer bark c. 0.1 mm thick, with reddish stripes on which pubescence near apex, becoming pale greyish or brownish and smooth when mature; inner bark c. 0.1 mm thick, blackish; wood pale brownish. Stipules triangular to subulate, 0.4–0.7 mm long, sericeous. Leaves clustered at the end of branchlets; petiole obtriangular and flat to slightly grooved above, 1–3 mm long, often glabrescent, lower side rounded and pubescent; blade oblanceolate or oblong, sometimes slightly asymmetric, 6–20 by 2.5–6 cm, membranous, base obtuse to cordate, without glands, margin distantly serrate, teeth falcate, apex acuminate or caudate, glabrous above, paler and more or less pubescent beneath; midrib slender, slightly raised on both sides, nerves 7–15 pairs, connected along margin, veinlets reticulate, obscure. Inflorescences bisexual, axillary, racemes, bracts to rachis stipule-like, main rachis 3–6 cm long, 0.25–0.5 mm diam, slightly pubescent, bracts lanceolate to oblong to linear, 1–2.8 by 0.3–0.5 mm, pubescent. Staminate flowers c. 4 mm diam; pedicel c. 2 mm long, c. 0.2 mm thick, pubescent; sepals oblanceolate or ovate, c. 1 by 0.6 mm, margin entire, ciliate, apex acute, outside pubescent; petals obovate, c. 1.8 by 1 mm, margin sometime ciliate, apex rounded, outer surface glabrous, inner rough and papillate; disc lobes semi-orbicular, c. 0.3 by 0.5, apex rounded; stamens 3, androphore c. 0.5 mm long, anthers free, ellipsoid, c. 0.5 mm long, opening yellowish, connectives dark reddish (when dried), with numerous droplets with secretion. Pistillate flowers c. 3.5 mm diam; pedicel slightly thickened towards apex, c. 4 mm long, apically c. 0.7 mm diam, accrescent when fruiting to up to 9 mm long and 1 mm diam, pubescent; sepals lanceolate, 1–1.5 by 0.5–0.7 mm, margin sometimes serrate, teeth glandular, apex acute, pubescent outside; petals as staminate flowers but caducous and slightly larger, 2–2.5 by 1–1.5 mm; disc lobes semi-orbicular, c. 0.55 by 0.45 mm, thin membranous, apex acute or rounded; ovary c. 0.8 mm diam, densely sericeous, style c. 0.1 mm long, almost indistinct, stigmas c. 0.5 mm long, completely bifid. Fruits c. 8 mm diam, finely pubescent; columella c. 4 mm long. Seeds not seen.

    Distribution — Java (endemic).

   ▼ = T. serratus; u = T. scopulatus; l = T. sinclairii; n = T. victoriae; « = T. wetriifolius; ▲ = T. wildeorum

    Habitat & Ecology — Rainforest. Flowering: November.

    Note — The young branches are reddish (in dried specimens) and pubescent. The outer bark regularly sheds off, and reddish stripes remain. In older parts the branches become pale greyish or brownish.

29. Trigonostemon sinclairii Jabl. (sect. Trigonostemon)

    Trigonostemon sinclairii Jabl., Brittonia 15 (1963) 154, Figs. 3, 4; Whitmore, Tree Fl. Malaya 2 (1973) 135; R.Y.Yu & Welzen, Blumea 62 (2018) 212, map 10; R.Y.Yu et al., Taxon 68 (2019) 929. — Type: SFN (Sinclair & Kiah bin Salleh) 40418 (holo SING), Malaya, Trengganu, Block 3B Gunong Tebu F.R., 51st mile Kuala Trengganu – Berut Road.

Shrubs or small trees, up to 5 m tall, stem sparsely branched, flowering branches 0.8–1.3 mm diam. Indumentum often of 2 layers of simple hairs, shortly villose and longer papillate-hispid. Outer bark 0.1–0.2 mm thick, often fissured, yellowish to brownish, villose and papillate-hispid; inner bark c. 0.5 mm thick, fibrous, dark brownish to blackish, with sap; sapwood 0.2–0.3 mm thick, yellowish to reddish brown; heartwood 0.4–0.7 mm diam, brownish. Stipules subulate, c. 1 mm long, caducous, often not seen. Leaves: petiole 4–15 cm long, villose and hispid; blade oblong, 20–45 by 8–17 cm, coriaceous, base obtuse or slightly cordate, with 2 adaxial glands, latter falcate or subulate, but often covered by long hairs, margin entire, often papillose-ciliate, apex acute to acuminate, or sometime rounded, both sides papillate-hispid; midrib raised and densely villose and hispid on both sides, nerves 15–20 pairs, slightly raised on both sides, curved and narrowed near margin, with two layers of hairs, villose and papillate-hispid, veins scalariform, papillate-hispid (only one layer, not villose), veinlets reticulate, obscure above. Inflorescences: staminate ones axillary, raceme-like thyrses, rachis up to 25 cm long, densely villose but sparsely hispid; bracts linear, 6–12 by 0.7–1 mm, hispid; pistillate inflorescences axillary, racemose, or sometimes sparsely branched at bottom, rachis sometimes hollow, up to 40 cm long, villose and hispid; bracts as staminate inflorescences, but larger, up to 20 by 2 mm. Staminate flowers c. 7 mm diam; pedicel 0.5–0.8 mm long, 0.2–0.4 mm diam, sparsely hispid; sepals lanceolate, 1.5–2 by 1–1.5 mm, apex acute, outside hispid and with a gland near apex, inside glabrous, sometimes with a few pale pustules on both sides; petals elliptic, c. 4.8 by 2.5 mm, base rounded, apex acute to rounded, dark reddish, contort, glabrous to often with sparsely pale pustules on both sides; disc glands rhomboid, 0.5–0.7 by 0.4–0.65 mm and c. 0.2 mm thick, apex acute, occasionally with sparsely pale pustules; stamens 3, androphore erect, c. 0.6 mm long, anthers ellipsoid, gathered on the top of androphore, 0.5–0.6 mm long, connectives with numerous apical pustules or droplets with secretion. Pistillate flowers (fruiting) 1–2 cm diam; pedicel 1–1.2 cm long, c. 1 mm diam, villose and sparsely hispid; sepals triangular, already enlarging, c. 2 by 1 cm, finally leaf-like, persistent, margin with few teeth near top, apex acuminate, both sides hispid and often villose or ciliate along veins and margins; petals not seen, caducous; disc lobes semi-orbicular, c. 0.4 by 0.7 mm; ovary densely hispid, styles c. 0.5 mm long, stigmas completely bifid, arms c. 0.8 mm long, bent. Fruits c. 1.5 cm diam, hispid outside; wall c. 0.6 mm thick, exocarp not splitting off; columella c. 6.5 mm long. Seeds c. 6.5 mm diam, often with sparse pustules on surface; hilum elliptic, c. 4 by 2 mm, apex often apiculate.

    Distribution — Malay Peninsula (endemic).

   l = T. sinclairii; u = T. scopulatus; ▼ = T. serratus; n = T. victoriae; « = T. wetriifolius; ▲ = T. wildeorum

    Habitat & Ecology — Primary forest to newly logged forest on hill side. Flowering: May and August; fruiting: July and September.

    Note — An extremely hairy species with large accrescent pistillate sepals.

30. Trigonostemon verticillatus (Jack) Pax (sect. Trigonostemon)

    Trigonostemon verticillatus (Jack) Pax in Engl., Planzenfam. IV.147.iii (1911) 87; Jabl., Brittonia 15 (1963) 164; Airy Shaw, Kew Bull. 26 (1972) 349; Whitmore, Tree Fl. Malaya 2 (1973) 136; Chantar.,Thai Forest Bull. (Bot.) 33 (2005) 30; in Santisuk & K.Larsen, Fl. Thailand 8, 2 (2007) 585, Pl. 31: 2; R.Y.Yu & Welzen, Blumea 62 (2018) 213, map 11; R.Y.Yu et al., Taxon 68 (2019) 928. — Enchidium verticillatum Jack, Malayan Misc. 2, 7 (1822) 90; Comp. Bot. Mag. 1 (1835) 257, excl. synon. Rumphius; Müll.Arg. in A.DC., Prodr. 15, 2 (1866) 1256; Merr., J. Arnold Arbor. 33 (1952) 224. — Neotype (designated here): A.C. Maingay 1403 (holo L; iso BM, K), Malay Peninsula, Malacca.

    Telogyne indica Baill., Étude Euphorb. (1858) 328, plate 11, fig. 13. — Trigonostemon indicus (Baill.) Müll.Arg., Linnaea 34 (1865) 214; in A.DC., Prodr. 15, 2 (1866) 1107; Hook.f., Fl. Brit. India 5 (1887) 398; Ridl., Fl. Malay Penins. 3 (1924) 264; Jabl., Brittonia 15 (1963) 152. — Type: Baillon, Étude Euphorb. (1858), Plate 11, Fig. 13.

Small trees, up to 8 m tall; flowering branches terete, 2.5–3 mm diam. Bark 0.4–0.5 mm thick, pale greyish; wood pale yellowish. Stipules subulate, 0.5–1.5 mm long, blackish and pubescent near base, yellowish at apex. Leaves: petiole wrinkled, terete but grooved above, 2–9 cm long, often thickened at apex and base; blade oblong, sometimes elliptic or lanceolate, occasionally linear, 10–22 by (1.5–)2.5–5 cm, chartaceous or coriaceous, base acute to rounded, 1 or 2 pairs of glands adaxially present, subulate or falcate, often glabrous, margin distantly serrate, teeth subulate, apex acuminate to caudate, upper surface dark green, lower surface pale green, both sides glabrous; midrib slightly raised above and distinctly elevated beneath, nerves 12–21 pairs, connected along margin, veinlets reticulate, often obscure. Inflorescences bisexual, terminal or subterminal, racemes (spike-like) or thyrses, often puberulent, main rachis up to 10 cm long, involucral bracts triangular to lanceolate to falcate, 1–2 by c. 0.5 mm, with 2 lateral bracteoles; bracts to flowers broadly triangular, somewhat sheathing, up to 1 by 1 mm, apex acuminate, puberulent. Staminate flowers c. 4 mm diam (unopened); pedicel slightly thickened towards apex, 1.5–3 mm long, apically 0.6–0.8 mm diam, glabrous or very slightly puberulent; sepals often unequal, orbicular to ovate, 1–1.5 by 1–1.5 mm, imbricate, apex rounded, outside glabrous or slightly puberulent, margin ciliate; petals ovate, 2.5–2.8 by c. 2 mm, dark reddish, contort, apex rounded, outer surface glabrous, inner surface rough and slightly papillose, margin entire, occasionally slightly ciliate; disc annular when young and cupular when mature, c. 0.5 mm wide, margin often with 5 notches; stamens 5, androphore c. 0.5 mm long, anthers ellipsoid, c. 1 mm long, divaricate, connectives apically with numerous droplets (or expanded cells) with secretion. Pistillate flowers c. 5 mm diam; pedicel as staminate flowers but longer and thicker, c. 4 mm long, c. 1 mm diam; sepals elliptic, c. 1.5 by 1 mm when flowering, more or less accrescent to 3 by 2 mm when fruiting, apex rounded, outside slightly puberulent, margin ciliate; petals as staminate flowers, caducous; disc annular, subentire; ovary 1.2–1.5 mm diam, puberulent, style c. 0.2 mm long, sometimes indistinct, stigmas c. 0.7 mm long, bifid at apex, arms c. 0.5 mm long, thickened abaxially, reniform at base. Fruits c. 1 cm diam, outside finely puberulent; wall 0.7–1 mm thick, exocarp detaching. Seeds c. 5.5 mm diam; hilum rhombic, c. 1.8 by 1 mm.

    Distribution — Vietnam, Thailand, Malay Peninsula.

    Note — The genus Enchidium, described by Jack (1822), is reliably identical to Trigonostemon, even though there were a few mistakes in the manuscript, e.g., he mentioned that the plants have 10 stamens, instead of 5. The genus remained monospecific since Jack’s publication. Jack’s original collection from Sumatra was never checked again by later botanists and it is very likely that it does not exist anymore (Merrill 1952). The illustration Jack cited (see Rumphius 1743) is a sterile plant and does not appear to be Trigonostemon.

Probably on account of the obscure status of Enchidium, botanists tended to abandon the name even though it was validly published prior to Trigonostemon. For example, Hooker (1887) regarded E. verticillatum as synonym under the later published T. indicus. Jackson (1893, 1895) reduced Enchidium as a synonym under Trigonostemon. Pax & Hoffmann (1911) also transferred the type species E. verticillatum to T. verticillatus and synonymised T. indicus under T. verticillatus. The genus was eventually rejected in 1954 (see Introduction).

Because Jack’s collection is not available and illustration is incorrect, a neotype is here designated to T. verticillatus. We followed Pax & Hoffmann’s (1911) treatment and the neotype specimen is chosen from one of Pax & Hoffmann’s (1911) vouchers.

Key to the varieties

 

1a.	Leaf blade oblong, elliptic or lanceolate, 10–22 by 2.5–5 cm. Petals with entire margin	a. var. verticillatus
1b.	Leaf blade nearly linear, 10–16 by 1.5–2.5 cm. Petals with a slightly ciliate margin	b. var. salicifolius

 

a. var. verticillatus

 

    Trigonostemon verticillatus (Jack) Pax var. verticillatus: R.Y.Yu & Welzen, Blumea 62 (2018) 213, map 11; Blumea 65 (2020) 44, map 14.

 

Leaves: blade oblong, elliptic or lanceolate, 10–22 by 2.5–5 cm. Petals with entire margin.

    Distribution — Vietnam, Thailand, Malay Peninsula.

 

   l  = T. verticillatus var. verticillatus; « = T. verticillatus var. salicifolius

 

    Habitat & Ecology — Primary dipterocarp forests on hillsides or near the sea, growing in peat swamps. Altitude: 60–400 m. Flowering: December to April.

 

b. var. salicifolius (Ridl.) Whitmore

 

    Trigonostemon verticillatus (Jack) Pax var. salicifolius (Ridl.) Whitmore, Gard. Bull. Singapore 26 (1972) 52; Fl. Malay Penins. 2 (1973) 136; R.Y.Yu & Welzen, Blumea 62 (2018) 213, map 11. — Trigonostemon salicifolius Ridl., Bull. Misc. Inform. Kew (1923) 366; Fl. Malay Penins. 3 (1924) 264; Jabl., Brittonia 15 (1963) 152, fig. 1; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 204. — Type: Ridley s.n. (holo K), Malaysia, Selangor, Kanching.

 

Leaves: blade nearly linear, 10–16 by 1.5–2.5 cm. Petals with a slightly ciliate margin.

    Distribution — Malay Peninsula (endemic).

 

   « = T. verticillatus var. salicifolius; l  = T. verticillatus var. verticillatus

 

    Habitat & Ecology — Dipterocarp forests. Altitude: 80–150 m. Flowering: January and July.

    Note — This is a tentative treatment, data from a molecular phylogeny is needed. The variety mainly differs from var. verticillatus by having narrower leaves.

31. Trigonostemon victoriae R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon victoriae R.Y.Yu & Welzen, Blumea 62 (2018) 215, fig. 15, map 10; R.Y.Yu et al., Taxon 68 (2019) 928; Blumea 65 (2020) 20, fig. 6, map 1. — Type: PNH (M.D. Sulit) 12317 (holo L), Philippines, Palawan Province, Victoria Mountains, Panacan, Aborlan.

Small trees, up to 6 m tall, dbh c. 10 cm; flowering branches 2–2.5 mm diam. Outer bark 0.1–0.2 mm thick, pale greyish, somewhat shiny, pubescent near apical buds and glabrescent in mature parts; inner bark 0.1–0.2 mm thick, dark reddish; wood pale yellowish. Stipules subulate, 0.5–1 mm long, often persistent, base pubescent, apex glabrous. Leaves: petiole terete but grooved above, 0.5–3 cm long, pubescent; blade elliptic, 6–11 by 2–4 cm, chartaceous to coriaceous, base acute to rounded, 2 adaxial glands present, often pubescent, margin distantly serrate, teeth glandular, apex acuminate to slightly caudate, upper side glabrous, dark red in dry specimens when young to pale grey and shiny when mature, lower side sparsely pubescent; venation penninerved, often pubescent on the lower side, especially in young leaves, midrib more or less raised above and elevated beneath, nerves 6–8 pairs, curved and narrowed along margin, veinlets reticulate. Inflorescences unisexual, racemose, staminate ones c. 5 cm long, c. 0.5 mm diam, appressed pubescent; bracts lanceolate to oblong, 1–3 by 0.3–0.6 mm, appressed pubescent; pistillate inflorescences often with only 1 flower at the top of inflorescences and sometimes a few depauperate buds below; peduncles up to 5 cm long, c. 0.5 mm diam, pubescent; bracts lanceolate to elliptic, 3–4 by 0.3–0.7 mm, pubescent. Staminate flowers (unopened) c. 3 mm diam; pedicel 0.5–1 mm long, c. 0.5 mm diam, pubescent; sepals ovate to elliptic, 1–1.5 by 0.8–1.1 mm, imbricate, margin entire, apex acute to acuminate, pubescent outside; petals orbicular, 0.9–1.1 mm diam, dark purplish, glabrous on both sides; disc lobes semi-orbicular, c. 0.2 by 0.1 mm, fleshy, apex acute; stamens 3, androphore indistinct, anthers ellipsoid, grouped at the top of androphore, c. 0.45 mm long. Pistillate flowers c. 4 mm diam; pedicel c. 3 mm long, c. 0.5 mm diam, sericeous; sepals lanceolate, 2.5–4 by 0.6–1.5 mm when flowering, accrescent to 10–13 by 2.5–4.5 mm when fruiting, margin with a few indistinct teeth, apex acute to acuminate, sericeous on both sides, denser outside; petals elliptic to ovate, 1.1–1.4 by 1–1.2 mm, glabrous except for ciliate margin; disc lobes rectangular, 0.15–0.2 by 0.2–0.25 mm, apex truncate, glabrous; ovary c. 0.65 mm diam, glabrous; styles c. 0.1 mm long, stigmas deeply divided and reniform, arms straight, c. 0.3 mm long. Fruits and seeds not seen.

    Distribution — Philippines (Victoria Mountains, endemic).

   n = T. victoriae; u = T. scopulatus; ▼ = T. serratus; l = T. sinclairii; « = T. wetriifolius; ▲ = T. wildeorum

    « = T. victoriae; l = T. filiformis; p = T. merrillii; n = T. palustris

    Habitat & Ecology — Dipterocarp forests, growing on clay, near rivers. Flowering: May.

    Note — Only known from the type collection. The mature leaves often turn greyish and are shiny, but this could be a drying artefact. Another useful distinction is that T. victoriae only has a few small bracts along the pistillate inflorescences while its resembling species, T. capillipes, tends to have larger, leaf-like bracts under the pistillate flowers.

32. Trigonostemon villosus Hook.f. (sect. Trigonostemon)

    Trigonostemon villosus Hook.f., Fl. Brit. India 5 (1887) 397; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 88; Ridl., Fl. Malay Penins. 3 (1924) 265; Jabl., Brittonia 15 (1963) 158; Whitmore, Tree Fl. Malaya 2 (1973) 135; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 204; Kew Bull. 36 (1981) 358; R.I.Milne, Kew Bull. 50 (1995) 37; R.Y.Yu & Welzen, Blumea 62 (2018) 215, fig. 16, 17, map 12, 13; R.Y.Yu et al., Taxon 68 (2019) 928. — Type: King’s collector s.n. (holo K), Malaya, Perak.

    Trigonostemon tomentellus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 89. — Type: Anonymous s.n. (holo SING, not found), Malacca.

    Trigonostemon carnosulus Airy Shaw, Kew Bull. 32 (1978) 415. — Type: CF (Yeop) 844 (holo K), Malaya.

    Trigonostemon polyanthus auct. non Hook.f.: R.I. Milne, Kew Bull. 50 (1995) 25.

Small trees, up to 6 m tall, dbh up to 6 cm; flowering branches 2.5–6 mm diam, buds pubescent. Outer bark 0.1–0.3 mm thick, pale brownish to greyish, often pubescent when young, glabrescent lower, sometimes fissured; inner bark 0.1–0.3 mm thick, dark reddish; sapwood 0.6–1.4 mm thick, pale yellowish; heartwood 0.6–1 mm diam, brownish, soft. Stipules subulate, 0.8–1.8 mm long, pubescent. Leaves: petiole terete but often furrowed above, 0.5–25 cm long, glabrous to hirsute, sometimes slightly thickened at base and apex; blade elliptic to oblong (Malay Peninsula, Borneo, Philippines) or oblanceolate (Sumatra), 6.5–32 by 2.5–14 cm, chartaceous, base cuneate, acute, obtuse or rarely slightly cordate (East Kalimantan), 2 adaxial glands present, margin distantly serrate, teeth small, subulate or falcate, apex acuminate to caudate, upper side glabrous, dark green, lower side paler and to a different extent villose; midrib flat or slightly raised above and distinctly elevated beneath; nerves 7–12(–15) pairs, often bow-shaped, narrowed along margin, veins reticulate, sometimes obscure. Inflorescences unisexual or bisexual, racemes (pistillate ones if unisexual) or thryses, sometimes condensed, often axillary, sometimes cauliflorous, villose; rachis up to 42 cm long, 0.3–0.9 mm diam, staminate flowers clustered into short cymes or glomerules along rachis, pistillate flowers often single per node; bracts linear to lanceolate, 0.8–3.2 by 0.2–1.1 cm, margin entire (Borneo, Philippines) or serrate (Malay Peninsula, Sumatra), glabrous to villose, bracteoles (Malay Peninsula) lanceolate to linear, up to c. 5.5 by 1 mm, villose. Staminate flowers 3.5–6 mm diam, pedicel 2–3.5 mm long, 0.2–0.3 mm diam, pinkish (Sabah), glabrous; sepals elliptic, 2–2.5 by 1–1.4 mm, imbricate, white (Sabah), margin ciliate, apex rounded, outer surface slightly pubescent, sometimes with a very faint gland near apex, inner surface glabrous or rarely slightly villose (only one collection, van Balgooy 2187, Malay Peninsula); petals elliptic to obovate to spathulate, 2–3.8 by 1–2 mm, purplish black, base often with a pinkish flame-like honey mark inside (Borneo), margin entire, apex rounded, smooth and glabrous outside, rough and papillose inside; disc lobes rectangular or obtrapezoid, c. 0.5 by 0.5 mm, yellowish (Sabah), apex truncate, sometimes reflexed; stamens 3, androphore 0.4–0.9 mm long, anthers ellipsoid, 0.5–0.6 mm long, pinkish (Sabah), connectives apically with numerous reddish droplets with secretion. Pistillate flowers 6–8 mm diam, pedicel often slightly thickened towards apex, 3.5–10 mm long, apically 0.5–1.2 mm diam, green or red, glabrous to hairy; sepals lanceolate (Malay Peninsula, Sumatra) or elliptic to oblong (Borneo, Philippines), 2.5–6 by 0.8–1 mm when flowering, sometimes accrescent when fruiting, up to c. 9 by 2.3 mm, white in flowers, turning green in fruits (Sabah), margin serrate (teeth often glandular, Malay Peninsula, Sumatra) to entire (Borneo, Philippines), apex acuminate, outer surface sparsely to densely villose, sometimes with a faint abaxial gland near apex, inner surface glabrous, very occasionally villose (one collection from Malay Peninsula); petals as staminate flowers but larger and caducous, 3–5 by 1.5–2.3 mm; disc rectangular, 0.3–0.9 by 0.5–0.6 mm, membranous, apex rounded or truncate; ovary c. 1 mm diam, glabrous to densely villose, styles short, indistinct, stigmas 3, completely bifid, free arm 0.8–1.3 mm long. Fruits c. 0.9–1.2 cm diam, villose; wall 0.4–0.6 mm thick; columella 4–6 mm long. Seeds 5–6.5 by 4.5–6.5 mm, hilum heart-shaped, 1.8–3.2 by 1.4–2.4 mm.

    Distribution — Malay Peninsula, Sumatra, Borneo, Philippines.

    Notes — 1. Milne (1995) misinterpreted T. polyanthus because he cited a wrong type specimen. The actual T. polyanthus is a very distinct species, differing from T. villosus in its penicillate or fastigiate inflorescences.

    2. This species consists of four varieties spreading over a huge area (Map 12, 13) of great morphological variation. We made this treatment based on a large number of collections showing that this massive variation actually connects all single forms together into a species complex, even though the extreme forms often do not resemble each other (see Fig. 18). These extremes, furthermore, have often become the source of synonyms, where the species status is only valid in the type locality, but in a larger area, intermediate forms are always found. As morphological discontinuities are the only valid argument for species / variety delimitation, all the forms in Fig. 18 are regarded as a single species despite the wide distribution; and T. villosus var. cordatus is described as a separate variety, regardless of its small distribution area (Sabah).

    3. Generally, the hairs on leaf surfaces, the size of petioles and leaf blades and the inflorescence structure can be good characters to tell the varieties apart.

The varieties villosus and borneensis all have relatively stable and similar leaf blade and petiole sizes (Fig. 16), but they are different in inflorescence and flower structures – in var. borneensis, the inflorescences are unisexual (versus bisexual in var. villosus, but staminate flowers often fall off), the pistillate inflorescences have fewer flowers (often fewer than 4) at a time (versus often more than 4 in var. villosus), and the pistillate sepals are not much accrescent and often have an subapical gland outside (versus obviously accrescent and with a faint or no gland in var. villosus).

The new variety cordatus has a hairy leaf blade, which forms a typical morphological discontinuity separating it from var. borneensis.

The variety merrillianus is different from var. borneensis by its much (variable) longer petioles, much larger blades, often leaf-like bracts and staminate flowers in condensed glomerules.

Key to the varieties

 

1a.	Petiole longer than 8 cm	d. var. merrillianus
1b.	Petiole shorter than 8 cm	2
2a.	.Inflorescences bisexual. — Malay Peninsula	a. var. villosus
2b.	Inflorescences unisexual	3
3a.	Leaves glabrous above. — Sumatra, Sabah, Philippines)	b. var. borneensis
3b.	Leaves pubescent above. — Sabah	c. var. cordatus

 

a. var. villosus

 

Trigonostemon villosus Hook.f. var. villosus: R.Y.Yu & Welzen, Blumea 62 (2018) 220, fig. 16, 18, map 13

 

   

 

Leaves: petiole 3–8 cm long; blade oblong, 12–18 by 3.5–5.5 cm, glabrous to glabrescent (rarely villose) above and villose beneath. Inflorescences bisexual or unisexual (often because staminate flowers fallen), thyrsoid, 6–16 cm long, one pistillate flower and a few staminate flowers per node, often more than 4 pistillate flowers present at one time. Staminate flowers: sepals often without a subapical gland; petals elliptic, honey mark unseen. Pistillate flowers: sepals lanceolate, apex acuminate, margin often serrate, always accrescent when fruiting; ovary villose. Fruits villose.

    Distribution — Malay Peninsula (endemic).

 

   u = T. villosus var. villosus; ▲ = T. villosus var. cordatus

 

    Habitat & Ecology — Understorey in primary forests to logged-over areas, often on hill sides or along rivers, growing in swamps forests, on peaty soil. Flowering: January, May, June, October, November; fruiting: January, April to June, October, November.

 

b. var. borneensis (Merr.) Airy Shaw

 

    Trigonostemon villosus Hook.f. var. borneensis (Merr.) Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 205; R.Y.Yu & Welzen, Blumea 62 (2018) 220, fig. 16, 18, map 12. — Trigonostemon borneensis Merr., Pl. Elmer. Born. (1929) 162; Jabl., Brittonia 15 (1963) 162; Whitmore, Tree Fl. Malaya 2 (1973) 136. — Type: Elmer 20742 (holo PNH, †; iso BM, K, L, SING, U), Borneo, near Tawao.

    Trigonostemon hirsutus C.B.Rob., Philipp. J. Sci. 6, Bot. (1911) 335; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 406; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 451; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47; R.I.Milne, Kew Bull. 50 (1995) 28, in key, 30, in key, 41, Fig. 3. — Type: BS (Robinson) 11798 (holo PNH, †, not seen), Philippines, Mindanao, Zamboanga District, Port Banga (synonymy somewhat doubtful as the type is lost.)

    Trigonostemon wenzelii Merr., Philipp. J. Sci. 8, Bot. (1913) 380; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.xiv (1919) 41; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 453. — Type: Wenzel 186 (holo PNH, †; iso L), Philippines, Leyte, Dagami.

    Trigonostemon villosus Hook.f. var. caesius R.I.Milne, Kew Bull. 50 (1995) 28, in key, 30, in key, 37. — Type: SAN (Ampuria) 40236 (holo K; iso SAN), Sabah, Beaufort District, Beaufort Hill.

 

   

 

Leaves: petioles 0.5–5.5 cm long; blade elliptic to obovate, 5.5–18 by 2.5–6.5 cm, glabrous above, often pubescent beneath. Inflorescences unisexual, up to 16 cm long, staminate ones racemose or thyrsoid, sometimes cauliflorous, a few flowers per node, never clustered as glomerules; pistillate ones racemose, often fewer than 4 flowers present at one time. Staminate flowers: sepals pink, often with a showy gland near the apex outside; petals obovate, with an orange to yellowish flame-like honey mark near the base. Pistillate flowers: sepals elliptic, margin entire; ovary villose. Fruits green when young, red when mature, glabrous to pubescent.

    Distribution — Sumatra, Borneo (Sabah), Philippines.

 

   « = T. villosus var. borneensis; l = T. villosus var. merrillianus

 

    Habitat & Ecology — Primary lowland rainforests, often on hillsides or near rivers, growing on well-drained brown loam soil. Flowering: June to December; fruiting: July to December.

    Note — Some collections from Sumatra (e.g., W.J.J.O de Wilde & B.E.E de Wilde-Duyfjes 19367, 21244, 21362) display an intermediate form between the variety villosus and variety borneensis. They have short petioles (shorter than 2.5 cm), seemingly unisexual inflorescences and often 1 or 2 pistillate flowers per inflorescence at one time, which all show clear allegiance to var. borneensis. Because of this, they are tentatively placed under var. borneensis even though there is a huge gap between their main distribution locations (Sumatra, Sabah), but the serrate sepals of the pistillate flowers with an acuminate apex do somewhat resemble var. villosus. 

 

c. var. cordatus R.Y.Yu & Welzen

 

    Trigonostemon villosus Hook.f. var. cordatus R.Y.Yu & Welzen, Blumea 62 (2018) 220, fig. 17, 18, map 13. ― Type: SAN (R.Y.Yu & Jemson) 158479 (holo L; iso SAN), Sabah, Sandakan, Kabili-Sepilok Forest Reserve.

 

 

Leaves: petiole 0.5–2.5 cm long; blade elliptic, 8.5–22 by 3.5–9.5 cm, often cordate at base, pubescent on both sides. Inflorescences unisexual, racemose or thyrsoid, 6–14 cm long, staminate flowers often cauliflorous, a few flowers per node along the rachis. Staminate flowers: sepals elliptic, white; petals claw-like, with a flame-like honey mark near the base. Pistillate flowers: sepals elliptic, green, apex rounded, margin entire, slightly accrescent in fruit; ovary glabrous to densely villose. Fruits green, pubescent.

    Distribution — Borneo (Sabah, endemic).

 

   ▲ = T. villosus var. cordatus; u = T. villosus var. villosus

 

    Habitat & Ecology — Lowland rainforests, often on ultramafic soil. Flowering: December to March; fruiting: December.

    Note — This variety is sometimes misidentified as T. merrillii because of the hairy leave surfaces, but from its racemose or thyrsoid inflorescences (very few flowers per node, certainly not short paintbrush-like glomerules as in T. merrillii) it easily differs from the latter species.

 

d. var. merrillianus (Airy Shaw) R.Y.Yu & Welzen

 

    Trigonostemon villosus Hook.f. var. merrillianus (Airy Shaw) R.Y.Yu & Welzen, Blumea 62 (2018) 220, fig. 18, map 12; R.Y.Yu et al., Blumea 65 (2020) 23, fig. 7, map 3. — Dimorphocalyx (?) borneënsis Merr., Philipp. J. Sci. 11, C. Bot. (1916) 73. ― Trigonostemon merrillianus Airy Shaw, Kew Bull. 25 (1971) 549, non T. borneënsis Merr.; Kew Bull., Addit. Ser. 4 (1975) 203. — Type: Hose 420 (holo K; iso L), Sarawak, 4th Division, Baram District, Entoyut River.

    Trigonostemon acuminatus Merr., Philipp. J. Sci. 11, Bot. (1916) 190; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.xiv (1919) 41; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 451; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 46. — Type: BS (Ramos) 24528 (holo PNH, †; iso BM, BO, K, L), Philippines, Samar, Catubig River.

    Trigonostemon laxiflorus Merr., Philipp. J. Sci. 16 (1920) 567; Enum. Philipp. Fl. Pl. 2 (1923) 451; Airy Shaw, Alphab. Enum. Euphorb. Philipp. Isl. (1983) 47. — Type: BS (Ramos & Edaño) 31097 (holo PNH, †; iso A, K, P, US) Philippines.

 

 

Leaves: petioles 1–25 cm long; blade ovate to elliptic, 8–32 by 2.5–14 cm, both sides often glabrous. Inflorescences unisexual, barely branched thyrses, up to 42 cm long, often with one large and leaf-like bract under each branch; staminate flowers often cauliflorous or in densely clustered glomerulus (Borneo) or cymes (Philippines) along a robust rachis; pistillate inflorescences racemose, robust and erect. Staminate flowers: sepals often with a faint to showy gland near the apex outside; petals sometimes with an orange to yellowish flame-like honey mark inside near the base. Pistillate flowers: sepals elliptic, entire to serrate, when serrate then teeth glandular; ovary often glabrous, occasionally slightly pubescent. Fruits pubescent.

    Distribution — Borneo, Philippines.

 

   l = T. villosus var. merrillianus; « = T. villosus var. borneensis   

 

    Habitat & Ecology — Understorey in primary to burned or logged-over forests, sometimes on hill tops or slopes or along riversides, growing on red clay loam soil. Altitude: 50–900 m. Flowering: February to June, October to December; fruiting: September to May.

    Note — This variety has the most variable petioles and leaf blades and more condensed staminate flowers on inflorescences: the plants from the Philippines have relatively shorter petioles, smaller blades and less condensed staminate flowers on each inflorescence node, whereas the plants from East and West Kalimantan have longer petioles (up to 25 cm long) and larger blades; in Sarawak (type locality) and Brunei, the plants have the most condensed glomerules along the staminate inflorescences. For more details, see Fig. 18. In fact, this massive variation was also seen by Milne (1995) when he tried to synonymise T. acuminatus, T. borneensis and T. merrillianus under T. polyanthus, although T. villosus (not T. polyanthus) is the correct species name.

33. Trigonostemon viridissimus (Kurz) Airy Shaw (sect. Tylosepalum)

    Trigonostemon viridissimus (Kurz) Airy Shaw, Kew Bull. 25 (1971) 545; Whitmore, Tree Fl. Malaya 2 (1973) 135; Airy Shaw, Kew Bull., Addit. Ser. 5 (1975) 205; Kew Bull. 36 (1981) 358; Kew Bull. 37 (1982) 36; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 48; R.I.Milne, Kew Bull. 50 (1995) 28, in key, 29, in key; R.Y.Yu & Welzen, Blumea 62 (2018) 221, map 14; R.Y.Yu et al., Taxon 68 (2019) 930; R.Y.Yu & Welzen, Blumea 65 (2020) 44. — Sabia viridissima Kurz, J. Asiac. Soc. Bengal part 2, 41 (1872) 304; Hook.f., Fl. Brit. India 2 (1876) 3; Kurz, Forest Fl. Burma 1 (1877) 301. — Blachia viridissima (Kurz) King, J. Asiac. Soc. Bengal 65 (1896) 455, in obs. — Kurziodendron viridissimum (Kurz) N.P.Balakr., Bull. Bot. Surv. India 8 (1966) 68, pl. 1, fig. 1–7. — Type: Kurz s.n. (holo K), India, Andamans.

    Trigonostemon ovatifolius J.J.Sm., Meded. Dep. Landb. 10 (1910) 583; Backer & Bakh.f., Fl. Java 1 (1963) 495. — Type: Koorders s.n. (holo BO?), Java.

    Trigonostemon membranaceus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 91. — Type: Koorders 32989 (holo BO), Java: Djapara.

    Trigonostemon sumatranus Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 90; S.Moore, J. Bot. 63, Suppl. (1925) 100 (as synonym of T. forbesii Pax = Wetria insignis (Steud.) Airy Shaw); Merr., Papers Mich. Acad. Sci. 20 (1935) 101; Jabl., Brittonia 15 (1963) 163 (see note under T. philippinensis); Stern, Amer. J. Bot. 54 (1967) 671; Whitmore, Fl. Malay Penins. 2 (1973) 135. — Type: Forbes 2647 (holo L; iso BM, K), Sumatra.

    Trigonostemon macgregorii Merr., Philipp. J. Sci. 16 (1920) 566; Enum. Philipp. Fl. Pl. 2 (1923) 452. — Type: BS (McGregor) 32424 (holo PNH, †; iso K, P, US), Philippines, Panay, Antique Province, Culasi.

Shrubs or small trees, up to 9 m tall, stem up to 10 cm diam; flowering branches 1.5–3 mm diam, sometimes hollow. Bark c. 0.3 mm thick, young parts pale and pubescent, sometimes with numerous oil-like spots, mature parts dark, brownish to greyish, glabrescent; wood pale yellowish. Stipules subulate to nipple-like, c. 0.5 mm long, caducous, often pubescent. Leaves: petiole terete but grooved above, 0.5–1.5(–5.5) cm long, wrinkled, pubescent; blade ovate to elliptic to oblong, sometimes lanceolate, 8–24 by 2.5–9 cm, membranous or chartaceous, often with numerous oil-like spots when young, base acute or obtuse, often with 1 or 2 pairs of adaxial glands, margin entire or slightly distantly serrate, apex acuminate to caudate, upper side glabrescent to glabrous, dark green, lower side often sparsely pubescent, paler and dull green; venations triplinerved, midrib and 2 basal nerves slightly raised above and well elevated beneath, often pubescent, especially near base, other nerves 6–10 pairs, bow-shaped and connected along margin, veins scalariform, veinlets reticulate. Inflorescences bisexual (but mostly unisexual), often axillary, loose paniculate, often with oil-like spots on young parts; main rachis terete, up to 25 cm long, c. 2 mm diam, slightly pubescent; branches slender and glabrescent; bracts lanceolate, up to 2 mm long, pubescent. Staminate flowers 5–9 mm diam; pedicel up to 9 mm long, c. 0.2 mm diam, glabrescent or slightly pubescent, often with numerous oil-like spots; sepals elliptic or orbicular, 1–1.5 by 0.6–1.2 mm, imbricate, margin somewhat undulate, apex rounded or truncate, often with a short notch, outer surface pubescent, often with numerous oil-like spots and a gland in the middle; petals obovate, 4–6.5(–10) by 3.5–4.5(–7) mm, contort, membranous, with several distinct parallel veins, base cuneate or somewhat claw-like, apex rounded, glabrous; disc annular, margin undulate, reflexed, sometimes with 5 notches; stamens 3, androphore 0.7–1.5 mm long, filaments 0.3–0.4(–0.6) mm long, anthers free, ellipsoid, 0.4–0.5 mm long. Pistillate flowers 5–9 mm diam, pedicel slightly thickened towards apex, 1–1.4 cm long, apically c. 0.5 mm diam when flowering, elongating up to 3 cm long and c. 1.4 mm diam in fruit, glabrescent, often with oil-like spots; sepals, petals and disc as staminate flowers, except petals caducous when fruiting; ovary 0.8–1 mm diam, glabrous, with numerous oil-like spots on surface, styles 0.2–0.6 mm long, stigmas 0.6–1.5 mm long, bent, slightly thickened and slightly bifid at apex. Fruits c. 1.5 cm diam, greenish, glabrous and with numerous oil-like spots, sepals persistent but not accrescent; wall c. 0.5 mm thick, exocarp detaching; columella c. 5 mm long. Seeds 7–8 mm diam, with numerous oil-like spots on surface; hilum rhombic, c. 1.5 by 1.2 mm.

    Distribution — China, India, Thailand, Laos, Vietnam, Malay Peninsula, Sumatra, Java, Borneo, Philippines, Lesser Sunda Islands.

    Habitat & Ecology — Primary to secondary forests, along coasts to hillsides, sometimes along rivers.

    Note — In addition to the Malesian region, this species is also found in China, India, Thailand, Laos and Vietnam under different names, all synonyms except viridissimus, which is the oldest and accepted epithet for this species.

Key to the varieties

 

1a.	Petioles often shorter than 1.5 cm, pubescent. Inflorescences axillary, pendulous, often pubescent	a. var. viridissimus
1b.	Petioles longer than 1.5 cm, glabrous. Inflorescences terminal or subterminal, erect, glabrous	b. var. elegantissimus

 

a. var. viridissimus

 

    Trigonostemon viridissimus (Kurz) Airy Shaw var. viridissimus: Airy Shaw, Kew Bull., Addit. Ser. 5 (1975) 205; R.Y.Yu & Welzen, Blumea 62 (2018) 221, map 14; Blumea 65 (2020) 45, map 15.

 

Leaves: petiole 0.5–1.5(–5) cm long, pubescent; blade elliptic to ovate, glabrescent above, pubescent beneath. Inflorescences often axillary, pendulous, often pubescent.

    Distribution — Malay Peninsula, Sumatra, Java, Borneo, Philippines, Lesser Sunda Islands.

 

   l = T. viridissimus var. viridissimus; « = T. viridissimus var. elegantissimus

 

    Habitat & Ecology — Growing on reddish clay soil. Altitude: 0–450 m. Flowering: all year round; fruiting: January, May, July, November.

    Note — A widely distributed variety with obvious triplinerved venation, paniculate inflorescences with few branches, free anthers (free parts of filaments often more than 0.3 mm long), glabrous ovary and often oil-like spots on the flowers and fruits.

 

b. var. elegantissimus (Airy Shaw) Airy Shaw

 

    Trigonostemon viridissimus (Kurz) Airy Shaw var. elegantissimus (Airy Shaw) Airy Shaw, Kew Bull., Addit. Ser. 5 (1975) 206; R.Y.Yu & Welzen, Blumea 62 (2018) 222, map 14; Blumea 65 (2020) 45, map 15. — Trigonostemon elegantissimus Airy Shaw, Kew Bull. 20 (1966) 48; Kew Bull. 32 (1978) 417; Whitmore, Tree Fl. Malaya 2 (1973) 135; R.I.Milne, Kew Bull. 50 (1995) 28, in key, 29, in key, 47. — Type: Kostermans 13695 (holo K; iso A, BO, K, L), E. Kalimantan, Sangkulirang District, Karangan River, near Batu Pondong.

    Trigonostemon sanguineus Gagnep., Bull. Soc. Bot. France 72 (1925) 470. — Type: E. Poilane 8201 (P, barcode P00717146, P, barcode P00717147), Vietnam, km 26 route from Nhatrang to Ninh Hoa.

 

Leaves: petiole 1.5–5.5 cm long, glabrous to slightly pubescent; blade oblong to lanceolate, glabrous above, glabrous to sparsely pubescent beneath. Inflorescences often terminal or subterminal, erect and firm, glabrous.

    Distribution — Vietnam, Malay Peninsula, Borneo.

 

   « = T. viridissimus var. elegantissimus; l = T. viridissimus var. viridissimus

 

    Habitat & Ecology — Growing on sandy loam to sandy stone. Altitude: 170–230 m. Flowering: March to September; fruiting: July, October.

    Note — The form elegantissimus is here recognized as a variety, following Airy Shaw (1975). The two varieties closely resemble each other in their floral structures, like the contort petals, the slender long and only shortly bifid stigmas. The length of the petiole and the shape of the leaf blade also show some overlap. Milne (1995) presents a good discussion on the differences between the two varieties although he treated them as two separate species.

34. Trigonostemon wetriifolius Airy Shaw & Ng (sect. Trigonostemon)

    Trigonostemon wetriifolius Airy Shaw & Ng, Malaysian Forester 41 (1978) 237; R.Y.Yu & Welzen, Blumea 62 (2018) 222, fig. 19, map 10; R.Y.Yu et al., Taxon 68 (2019) 929. — Type: KEP FRI (F.S.P. Ng) 27157 (holo K; iso KEP), Malaysia, S Pahang, Lesong Forest Reserve in proposed Endau-Rompin National Park.

Small trees, 3 m tall, stem single, erect, 10–12 mm thick; flowering branches up to 1.2 cm diam, adventitious roots present, 0.5–1 mm thick, puberulent. Bark c. 0.6 mm thick, brownish to greyish, smooth to fissured; sapwood c. 2 mm thick, yellowish; heartwood 3–4 mm diam, whitish. Stipules subulate, 3–4 by c. 1 mm, apex acute, puberulent, caducous. Leaves clustered on the top of the stem; petiole c. 1.8 cm long, c. 5 mm diam, slightly pubescent; blade spathulate to oblanceolate, 35–62 by 9–19 cm, chartaceous, base rounded, adaxial glands not seen, margin distantly serrate, apex acuminate, both sides glabrous; venation penninerved, slightly pubescent on lower side, midrib robust, slightly raised on both sides, nerves 27–30 pairs, curved, veins scalariform, veinlets reticulate. Inflorescences axillary, 1–3 cm long, few-flowered, 1 pistillate flower at top and a few staminate flowers below, rachis appressed puberulent; bracts subulate, 1–5 mm long, puberulent. Staminate flowers c. 4 mm diam; pedicel 1–2 mm long, glabrous; sepals rounded to ovate, 2–3 by 1–2 mm, apex obtuse, pubescent outside, inside glabrous; petals ovate, 1–1.5 by 1–1.5 mm, fleshy, glabrous, yellowish except reddish at base, apex obtuse; disc lobes more or less square, fleshy, c. 0.3 by 0.5 mm; stamens 5, androphore short, hidden, anthers ellipsoid, c. 0.5 mm long, divaricate at apex. Pistillate flowers (unopened): pedicel, sepals, petals and disc as staminate flowers; ovary glabrous; styles short, stigmas slightly bifid. Fruits and seeds unknown.

    Distribution — Malay Peninsula (Lesong Forest Reserve, endemic).

   « = T. wetriifolius; u = T. scopulatus; ▼ = T. serratus; l = T. sinclairii; n = T. victoriae; ▲ = T. wildeorum

    Habitat & Ecology — Primary lowland forest under logging. Flowering: September.

    Note — Only known from the type specimen. Two slides of the plant (see Fig. 19, taken by Francis Ng) are attached with the type specimen. Descriptions of staminate flowers are mainly based on the slides, thus the measurements might not be exactly accurate, since a scale was unavailable; other parts of descriptions are based on Airy Shaw & Ng (1978). The species resembles T. detritiferus in morphology and living strategy, for more details, see notes under T. detritiferus.

35. Trigonostemon wildeorum R.Y.Yu & Welzen (sect. Trigonostemon)

    Trigonostemon wildeorum R.Y.Yu & Welzen, Blumea 62 (2018) 222, fig. 20, map 10; R.Y.Yu et al., Taxon 68 (2019) 929. — Type: W.J.J.O de Wilde & B.E.Ede Wilde-Duyfjes 20274 (holo L; iso BO), Indonesia, North Sumatra, Atjeh, Middle Alas River (Lae Sauraya) area, c. 15 km N. of Gelombang, S. of Bengkong River, 2° 55' N,99° 57' E. 

Small trees, 2–4.5 m tall; flowering branches 1.5–3 mm diam, buds golden sericeous. Bark c. 0.3 mm thick, pale greyish, appressed sericeous to hirsutulous when young, often smooth and fissured when mature; sapwood c. 2 mm thick, brownish; heartwood c. 2 mm diam, whitish. Stipules subulate, 0.5–0.6 mm long. Leaves: petiole terete, 0.5–1 cm long, flat above, rounded beneath, appressed hirsutulous; blade obovate, 7.5–22 by 3.5–7.5 cm, chartaceous to coriaceous, base cuneate to acute, 2 adaxial glands present, these subulate to falcate, caducous, margin entire to distantly serrate, ciliate, teeth small and falcate, apex caudate, tip 0.8–2.5 cm long, sometimes slightly slanting, upper side dark brownish (when dry), sparsely sericeous when young, pale brownish to greyish (when dry), glabrescent when mature, lower side brownish, sparsely sericeous; venation penninerved, midrib flat above and elevated beneath, hirsutulous to sericeous on both sides, nerves 8–12 pairs, straight, branched and slightly curved along margin, often hirsutulous beneath, veinlets reticulate. Inflorescences reduced to a cauliflorous fascicle of at most 3 flowers; bracts oblong to linear, 1–2.5 by 0.3–0.5 mm, hirsutulous. Staminate flowers c. 6 mm diam; pedicel c. 0.5 mm long, 0.3–0.4 mm diam, densely hirsutulous; sepals elliptic, 1.5–2 by 0.8–1.3 mm, base connate, margin entire, apex acute to rounded, outside densely sericeous to hirsutulous, inside slightly floccose; petals obovate, c. 3.5 by 2.5 mm, dark purplish black, base slightly claw-like, entire, apex rounded, glabrous on both sides, few dark palmate veins often visible; disc lobes semi-orbicular, 0.4–0.5 by 0.6–0.8 mm, apex sometimes with a shallow notch; stamens 5, monadelphous, androphore erect, c. 1 cm long, c. 0.3 mm diam, anthers free, ellipsoid, divaricate, each theca c. 0.5 by 0.3 mm. Pistillate flowers c. 5 mm diam (not fully opened); pedicel c. 1 mm long, apically c. 1 mm diam, slightly thickened near apex, densely pubescent; sepals triangular, 3–3.5 by 1.5–2.5 mm, base narrowed and connate, margin serrate, apex acuminate, outside densely hirsutulous to sericeous, inside hirsutulous to pubescent, accrescent in fruits, then elliptic to ovate, up to 1.3 by 1 cm, base rounded to truncate, margin distantly serrate, apex acute, sometimes with a small notch, outside a few palmate veins visible, sericeous especially on veins, inside sparsely sericeous; petals ovate to elliptic, c. 2.5 by 1.5–2 mm, dark purplish black, caducous, margin entire, apex acute to acuminate, glabrous; disc lobes as staminate flowers; ovary c. 0.8 mm diam, densely pubescent, style indistinct, stigmas c. 0.9 mm long, deeply bifid, arms c. 0.7 mm long, thickened and slightly sagittate at base. Fruits c. 1 cm diam, puberulent outside; wall c. 0.5 mm thick, exocarp partly splitting off; columella c. 5 mm long. Seeds c. 6 mm diam.

    Distribution — Sumatra (endemic).

   ▲ = T. wildeorum; u = T. scopulatus; ▼ = T. serratus; l = T. sinclairii; n = T. victoriae; « = T. wetriifolius

    Habitat & Ecology — Primary foothill forest on yellow-red loamy soil over basalt rock. Altitude: 50–200 m. Flowering and fruiting: July.

    Note — Only known from the two collections mentioned above.

Doubtful Species

36. Trigonostemon angustifolius Merr.

    Trigonostemon angustifolius Merr., Philipp. J. Sci. 20 (1922) 396; R.Y.Yu & Welzen, Blumea 62 (2018) 224, map 15. — Type: BS (Ramos & Edaño) 36764 (of 36560) (holo PNH, †; iso K), Philippines, Mindanao, Zamboanga Disrict, Malangas.

Shrubs, 1–3 m tall; flowering branches c. 3 mm diam. Outer bark c. 0.1 mm thick, white to grey, smooth, slightly pubescent when young, glabrescent; inner bark 0.2–0.3 mm thick, dark brownish; wood white to yellow. Stipules very small, pointing, appressed pubescent, caducous. Leaves: petiole terete but grooved above, 5–8 mm long, 1.2–1.5 mm diam, appressed pubescent; blade oblong, 10–15 by 2–3 cm, chartaceous, base acute, glands not seen, margin distantly serrate, teeth glandular, apex acuminate to shortly caudate, upper surface dark brown to black (when dry), glabrous, lower surface reddish brown, slightly pubescent; midrib slightly raised and glabrous above, distinctly elevated and pubescent beneath, nerves 8–11 pairs, pubescent beneath, veins reticulate, obscure above. Inflorescences: staminate ones not seen; pistillate ones axillary, slender, peduncled, a glomerule at apex; peduncle c. 5 cm long, c. 0.5 mm diam, appressed pubescent; glomerules few-flowered, subtended by two bracts (also one bract present on the lower node), bracts lanceolate, 10–12 by 2–3 mm, appressed pubescent beneath. Staminate flowers not seen. Pistillate flowers: sepals lanceolate, c. 6 by 2.5 mm, apex acuminate, outside eglandular, slightly pubescent; petals 5–6 mm long, glabrous, dark purple; ovary glabrous, styles 3, stigmas cleft nearly to the base, arms linear, 1.5 mm long, acuminate. Fruits depressed globose, c. 12 mm diam, brown, sparingly appressed pubescent, sepals accrescent up to 12 by 6 mm. Seeds not seen.

    Distribution — Philippines (Mindanao, endemic).

   l = T. angustifolius; « = T. cumingii; n = T. stenophyllus; ▲ = T. whiteanus

    Habitat & Ecology — On forested slopes at low altitudes (Merrill 1922). Flowering: October.

    Vernacular name — Pululi (Merrill 1922).

    Note — The species is only known from the type collection. Due to the insufficient material seen the descriptions of pistillate flowers and fruits are based on Merrill (1922). Knowledge on the staminate flowers of the species is still lacking and, therefore, it is impossible to even determine whether the species belongs to Trigonostemon or not.

37. Trigonostemon stenophyllus Quisumb. 

    Trigonostemon stenophyllus Quisumb., Philipp. J. Sci. 41 (1930) 330, Fig. 8; R.Y.Yu & Welzen, Blumea 62 (2018) 225, map 15. — Type: BS (Ramos & Edaño) 47331 (holo PNH, †; iso A, K, NY), Philippines, Luzon, Isabela Prov., Mount Moises.

Shrubs, up to 1 m tall; branches terete, 2–3.5 mm diam, pubescent when young, glabrous when mature. Stipules unknown. Leaves: petioles 1–4 cm long, somewhat pubescent; blade oblong to lanceolate, 5.5–16.5 by 1–2.5 cm, chartaceous, base acute to obtuse, margin entire to slightly distantly serrate, apex acuminate, upper surface brown to dark brown when dry, glabrous, lower surface paler and sparsely pubescent; midrib flat above and elevated beneath, nerves 6–11 pairs, veinlets reticulate. Inflorescences: staminate ones unknown; pistillate ones axillary, racemose, up to 5.5 cm long, pubescent; bracts narrowly lanceolate, 3–4 mm long. Staminate flowers unknown. Pistillate flowers c. 4.5 mm diam; pedicels slightly thickened towards apex, c. 9.5 mm long, apically c. 0.6 mm diam, appressed pubescent; sepals oblong to lanceolate, c. 3 by 0.7 mm, margin entire, apex acute to acuminate, appressed pubescent outside, glabrous inside; petals oblong-obovate, c. 5 by 2 mm, apex rounded, glabrous; disc lobes elliptic, c. 0.5 by 0.3 mm, apex rounded, glabrous; ovary c. 0.95 mm diam, densely pubescent; styles 0.1–0.2 mm long; stigma linear, c. 1.3 mm long, deeply bifid into 2 arms, each arm c. 1 mm long, slightly thickened near base. Fruits c. 1.2 cm diam, brown, sparsely puberulent, persistent sepals not accrescent; wall c. 0.35 mm thick, exocarp partly detaching. Seeds c. 7 mm diam.

    Distribution — Philippines (endemic).

   n = T. stenophyllus; l = T. angustifolius; « = T. cumingii; ▲ = T. whiteanus

    Note — The species is only known from the type. The description is based on Quisumbing (1930). Due to the insufficient specimen seen, especially the lack of staminate flowers, the species is regarded doubtful here. It is probably a synonym of T. filiformis.

38. Trigonostemon whiteanus (Croizat) Airy Shaw

    Trigonostemon whiteanus (Croizat) Airy Shaw, Kew Bull. 38 (1983) 68; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 48; R.Y.Yu & Welzen, Blumea 62 (2018) 225, map 15. — Cheilosa whiteana Croizat, J. Arnold Arbor. 23 (1942) 507; Airy Shaw, Kew Bull. 16 (1963) 365, in note. — Type: FB (Curran) 17733 (holo A, iso K), Philippines, Luzon, Pampanga Prov., Mt. Arayat.

Shrubs or trees; flowering branches c. 3 mm diam. Bark 0.3–0.4 mm thick, blackish, smooth, lenticellate, appressed pubescent when young, glabrous when mature; wood yellowish. Stipules not seen (see note 2). Leaves: petiole furrowed above, rounded beneath, 3–5.5 cm long, 1.2–1.5 mm diam (middle part), slightly thickened at base and apex, slightly pubescent above, glabrous beneath; blade broad ovate, 9–13 by 6.5–9 cm, thin coriaceous, base rounded, with 2 adaxial glands, slightly hairy, margin entire, apex acute to acuminate, yellowish green above (when dry), pinkish brown beneath, both sides glabrous; venations triplinerved, midrib slightly raised above and distinctly elevated beneath, nerves 4–7 pairs, curved, slightly raised on lower side, veinlets reticulate. Inflorescences: staminate ones not seen; pistillate ones few branched, pyramidal, densely appressed pubescent, up to 7 cm long and 2.5 mm diam; bracts triangular, 1.5–3 by 1–1.5 mm, apex acuminate, densely appressed pubescent outside, glabrous inside. Staminate flowers not seen. Pistillate flowers 3.5–4.5 mm diam; pedicel 4–6.5 mm long, 0.45–0.8 mm diam, appressed pubescent; sepals triangular to lanceolate, 2–2.5 by 0.8–1.2 mm, apex acuminate, appressed pubescent outside; petals fallen, remnants membranous, yellowish, glabrous; disc lobes c. 0.5 mm wide, appressed pubescent; ovary 2–2.2 mm diam, densely appressed pubescent; style c. 0.5 mm long, trifid, stigma 0.7–0.8 mm long, branches basally connate, apex very slightly thickened and bifid. Fruits and seeds unknown.

    Distribution — Philippines (endemic).

   ▲ = T. whiteanus; l = T. angustifolius; « = T. cumingii; n = T. stenophyllus

    Notes — 1. Only known from the type collection. No staminate flowers are available, which makes the generic identification uncertain, but the petals and trifid styles are typical for Trigonostemon, though not exclusively.

    2. The development of the stipules seemed to be constrained, only two very obscure elevations with a few hairs were found instead of normal stipules.

Excluded Names

    Trigonostemon arboreus Ridl., Bull. Misc. Inform. Kew (1928) 75. — Type: KEP (Nur or Henderson) 18595 (holo SING), Malay Peninsula, Pulau Tioman, Sedagong. = Omphalea malayana Merr. (Milne, Kew Bull. 50, 1995).

    Trigonostemon asahanensis Croizat, J. Arnold Arbor. 23 (1942) 54. — Type: Rahmat Si Boeea 9872 (L), Sumatra, Asahan, vicinity of Tomoean Dolok. = Tritaxis muricata (Hook.f.) R.Y.Yu & Welzen (Yu et al., Taxon 68, 2018: 933).

    Trigonostemon bulusanensis Elmer, Leafl. Philipp. Bot. 10 (1939) 3735; Airy Shaw, Kew Bull. 20 (1967) 413. — Dimorphocalyx bulusanensis (Elmer) Airy Shaw, Kew Bull. 27 (1972) 92. — Type: Elmer 17296 (K, L), Philippines, Luzon, Prov. of Sorsogon, Irosin (Mt Bulusan). = Tritaxis malayana (Hook.f.) R.Y.Yu & Welzen (Yu et al., Taxon 68, 2018: 933).

    Trigonostemon forbesii Pax in Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 88; S.Moore, J. Bot. 43 (1925) 100; Jabl., Brittonia 15 (1963) 165. — Type: Forbes 1892 (GH, L), Indonesia, Sumatra, Lampong, Mt Tengamoes (= Gunung Tanggamus). = Wetria insignis (Steud.) Airy Shaw (Van Welzen, Blumea 43, 1998: 157).

    Tritraxis macrophylla Müll.Arg., Flora 47 (1864) 482. — Trigonostemon macrophyllus (Müll.Arg.) Müll.Arg., Linnaea 34 (1865) 213. — Ostodes macrophylla (Müll.Arg.) Benth. ex Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 18; Ridl., Fl. Malay Penins. 3 (1924) 269, f. 153. — Type: Griffith 4788 (holo K), Malacca. = Paracroton pendulus (Hassk.) Miq. (Esser in Welzen & Chayam., Euphorbiaceae (Genera G‒Z); in: Santisuk & K.Larsen, Fl. Thailand 8, 2, 2007: 468).

    Trigonostemon oliganthum K.Schum. in K.Schum. & Lauterb., Nachtr. Fl. Schutzgeb. Südsee (1905) 298. — Type: Nyman 554 (holo UPS), Kaiser-Wilhelmsland [= Papua New Guinea], Sattelberg. = Cleidion papuanum Lauterb. (Kulju & Van Welzen, Blumea 50, 2005: 212).

    Tritaxis zeylanicus Müll.Arg., Flora 47 (1864) 482. — Trigonostemon zeylanicus (Müll.Arg.) Müll.Arg., Linnaea 34 (1865) 213. — Type: not designated, cultivated in garden. = Paracroton zeylanicus (Müll.Arg.) N.P.Balakr. & Chakrab. (Balakrishnan & Chakrabarty, Kew Bull. 48, 1993: 723).