Malesian Euphorbiaceae Descriptions

104. TRITAXIS (Euphorbiaceae)

P.C. van Welzen, A.F. van Oostrum, F.J.W. SLik, R.-Y. Yu

van Welzen, P.C. & van Oostrum, A.F. 2015. Revision of Malesian species of Dimorphocalyx (Euphorbiaceae). Blumea 59: 191–201.

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

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Genus description

Key to the species

Species description

Dubious name

Excluded taxa

Tritaxis Baill.

    Tritaxis Baill., Étude Euphorb. (1858) 342; Benth. in Benth. & Hook.f., Gen. Pl. 3 (1880) 292; Pax in Engl., Planzenr. IV.147 (1910) 113; R.Y.Yu, Slik & Welzen, Taxon 68 (2019) 932. — Trigonostemon Blume sect. Tritraxis (Baill.) Müll.Arg., Linnaea 34 (1865) 213; in DC., Prodr. 15, 2 (1866) 1107. — Type: Tritaxis gaudichaudii Baill.

    Dimorphocalyx Thwaites, Enum. Pl. Zeyl. (1861) 278; Benth. in Benth. & Hook.f., Gen. Pl. 3 (1880) 301; Hook.f., Fl. Brit. India 5 (1887) 403; Trimen, Handb. Fl. Ceylon 4 (1898) 54, pl. 84; Brandis, Ind. Trees (1906) 581; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 31; Ridl., Fl. Malay Penins. 3 (1924) 266; Gagnep. in Lecomte, Fl. Indo-Chine 5 (1925) 295; Pax & K.Hoffm. in Engl. & Harms, Nat. Pflanzenfam., ed. 2, 19c (1931) 158; Airy Shaw, Kew Bull. 20 (1967) 412; Kew Bull. 23 (1969) 123; Kew Bull. 26 (1972) 251; Kew Bull. 27 (1972) 92; Whitmore, Tree Fl. Malaya 2 (1973) 86; Airy Shaw, Kew Bull. 29 (1974) 328; Kew Bull. Addit. Ser. 4 (1975) 95; Kew Bull., Addit. Ser. 8 (1980) 73; Muelleria 4 (1980) 237; Kew Bull. 35 (1980) 624; Kew Bull. 36 (1981) 286; Kew Bull. 37 (1982) 16; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20; Chakrab. & N.P.Balakr., Proc. Indian Acad. Sci. 100 (1990) 286; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 106; Philcox in Dassan., Fl. Ceyl. 11 (1997) 107; Radcl.-Sm., Gen. Euphorbiacearum (2001) 300; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1 (2005) 229; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 174; Welzen & Oostrum, Blumea 53 (2015) 193. — Trigonostemon Blume sect. Dimorphocalyx (Thwaites) Müll.Arg., Linnaea 34 (1865) 212; in DC., Prodr. 15, 2 (1866) 1105. — Type: Dimorphocalyx gabellus Thwaites [= Tritaxis glabella (Thwaites) R.Y.Yu & Welzen] 

    Trigonostemon Blume Sect. Anisotaxis Müll.Arg., Linnaea 34 (1865) 213; in DC., Prodr. 15, 2 (1866) 1107. — Type: Trigonostemon cumingii Müll.Arg. [= Tritaxis cumingii (Müll.Arg.) Benth.]

Treelets to trees, dioecious (seldom monoecious). Indumentum of simple hairs, usually on young parts only. Stipules small, triangular, caducous. Leaves simple, alternate, petiolate, symmetric, margin entire to serrulate to serrate, with glands abaxially in the teeth or near the margin when entire; venation pinnate, slightly raised (to slightly sunken) above, raised below, secondary veins looped and joined near the margin, tertiary veins reticulate (or scalariform), veinlets reticulate. Inflorescences axillary or terminal, short, cymose, thyrsoid or narrowly paniculate when staminate, more or less racemose when pistillate, staminate flowers few together in cymose groups, pistillate flowers usually single per node or per inflorescence; bracts triangular to leaf-like. Flowers regular, 5-merous; calyx cup-shaped, (4)5(6)-lobed, lobes imbricate; petals 5, longer than calyx, imbricate, white. Staminate flowers: disc glands 5, free or zig-zagging around free stamens; stamens (7–)10–15(–c. 20), in 3 whorls, outer free, inner 2 with filaments connate into an androphore, anthers ellipsoid, dorsifixed, opening introrse via a lengthwise slit, thecae 2, parallel; pistillode absent. Pistillate flowers: petiole slightly broadening towards apex; disc annular; ovary ovoid, 3-locular, ovules 1 per locule, style generally absent, stigmas apically split. Fruits 3-lobed capsules, subglobose, dehiscing septicidally and (partly) loculicidally into separate or 2-valved cocci; pedicels elongating; sepals enlarging and enclosing fruit; wall thinly woody, exocarp often detaching; columella persistent, T-shapeDimorphocalyx Seeds dry, obovoid, ecarunculate.

    Distribution — A genus of ca. 13 species, in S.E. Asia from Sri Lanka to Hainan to Australia. Eight species are recognised for Malesia.

Key to the species

1. Tritaxis australiensis S.Moore 

   Tritaxis australiensis S.Moore, J. Linn. Soc., Bot. 45 (1920) 218; R.Y.Yu et al., Taxon 68 (2019) 932. — Syntypes: Damel s.n. (BM, not seen, BRI, K), Australia, Queensland, Cape York, Cook pastoral district.

    Dimorphocalyx australiensis C.T.White, Proc. Roy. Soc. Queensl. 47 (1936) 80; Airy Shaw, Kew Bull. 23 (1969) 125; Kew Bull. 29 (1974) 328; Kew Bull., Addit. Ser. 8 (1980) 74; Muelleria 4 (1980) 237; Kew Bull. 35 (1980) 624; Kew Bull. 37 (1982) 16; Welzen & Oostrum, Blumea 53 (2015) 194, fig. 1c, map 1. — Type: Brass 2019 (holo BRI; iso A, K, 2 sheets, US), Australia, Queensland, Mowbray River.

    [Croton muricatus Zipp. ex Span., Linnaea 15 (1841) 348, nom. nud. — Based on: Zippelius s.n. (L, 3 sheets, barcodes: L  0245271, L  0245278, L  0245277), (Indonesia, Lesser Sunda Islands,) Timor.]

Shrubs to small trees, to 10 m high, d.b.h. to 20 cm; flowering branches 1–2 mm thick, round to somewhat angular, yellow to brown, mainly slightly hairy at nodes, usually striate. Indumentum of ferrugineous hairs, most parts mainly glabrous. Outer bark (greenish) brown to grey, rough, sometimes flaky, c. 0.5 mm thick; under bark red; inner bark orange-brown to reddish brown to light brown, c. 7 mm thick; sapwood cream to pale brown. Stipules triangular, c. 5 by 1.5 mm, outside hairy, very early caducous, usually absent. Leaves: petiole 0.4–2.7 cm long, 0.7–1.5 mm diam, glabrous to slightly hairy, often transversely cracked when dry, basically and apically pulvinate; blade (ovate to) elliptic (to obovate), widest in ± middle, 2.3–14.3 by 1.5–6.5 cm, 1.3–2.2 times as long as wide, papyraceous, base obtuse to round to cuneate to attenuate, margin ± entire to serrulate, revolute, apex (rounded) to acuminate (to cuspidate), upper surface dark green, lower surface lighter green, venation slightly raised above, raised below, secondary veins (6–)8–12 pairs, tertiary nerves reticulate. Inflorescences axillary to mainly terminal, very short, dichasial, to 6 cm long, branches round to angular, partly to completely densely sericeous; bracts and 2 bracteoles forming tight cups, 1.1–1.9 by 1.1–2.2 mm, hairy outside, coriaceous, midrib thickened, apex mucronulate. Staminate flowers c. 15 mm in diam, white, buds green; pedicel 3.5–7 mm long above abscission zone, round, hairy; calyx connate at base, lobes ovate to obovate, 1.7–2.5 by 2–2.5 mm, apex round, outside hairy except margin, inside glabrous, without subapical glands outside; petals oblong to obovate, 6.5–8.3 by 3.2–5.3 mm, basally with a nail of c. 0.7 mm, apex round, nail and basal margins thickened and hairy outside, rest glabrous; disc 5 thick, short lobes, 0.6–1 by 0.5–0.6 mm, glabrous; stamens 7 or 8, in 2 whorls, all filaments partly united, glabrous, basal part of androphore of outer 4 or 5 stamens c. 3.5 mm long, free part of filaments c. 1.3 mm, inner part of androphore of inner 3 stamens c. 5.2 mm long, free part of filaments c. 0.5 mm, anthers 0.5–1 by 0.5–0.9 mm, dorsifixed. Pistillate flowers 6–7 mm in diam, white; pedicel 5–8 mm long above abscission zone, round to flattened, hairy, glabrescent; calyx (4)5-lobed, lobes, ovate, 2.3–3.5 by 2–3 mm, outside and inside sericeous, without subapical glands outside; petals very early caducous; disc a thin ring, glabrous; ovary ovoid, 2.5–3 by 2–3 mm, densely set with slender, pointed spines, hairy, style absent to 0.7 mm long, stigmas 1.3–2 mm long, upper 0.3–1 mm split. Fruits 9–10 by 6–6.5 mm, echinate, hairy, green to dark brown; pedicel 6–10 mm long; sepals enlarging to 4 by 2 mm; wall c. 0.8 mm thick, woody, exocarp not splitting off; columella 4–4.5 mm long. Seeds ellipsoid to obovoid, c. 5.3 by 4 by 4 mm, slightly marbled.

    Distribution — Lesser Sunda Islands (Sumbawa, Flores, Timor), New Guinea, Australia (Queensland) (Airy Shaw, 1980).

l = T. australiensis (« = T. moluccensis; u = T. pauciflora; n = T. trichocarpa)

    Habitat & Ecology — In monsoon forest to complex notophyll vine forest to the substage of primary rain forest, but also in scrubs; often in wetter areas, but also dry slopes; found on metamorphic rocks (tuff breccia) to soils derived from basalt. Altitude: 10–800 m. Flowering: whole year through; fruiting: January, October, December (probably also whole year through).

    Vernacular name — Lesser Sunda Islands: Flores: Anak watu.

2. Tritaxis cumingii (Müll.Arg.) Benth.

    Tritaxis cumingii (Müll.Arg.) Benth., J. Linn. Soc., Bot. 17 (1878) 221; Pax in Engl., Pflanzenr. IV.147.i (1910) 114; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 449; R.Y.Yu et al., Taxon 69 (2019) 932; R.Y.Yu & Welzen, Blumea 65 (2020) 47. — Trigonostemon cumingii Müll.Arg., Linnaea 34 (1865)  213; in DC., Prodr. 15, 2 (1866) 1107; R.Y.Yu & Welzen, Blumea 62 (2018) 224, map 15. — Dimorphocalyx cumingii (Müll.Arg.) Airy Shaw, Kew Bull. 23 (1969) 124; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20; Welzen & Oostrum, Blumea 53 (2015) 199.. —  Type: Cuming 1693 (holo G-DC, iso BM, E, G, K, L, P), Philippines.

Shrubs, 0.3–0.5 m tall, dbh up to 4 cm; flowering branches 1–2.9 mm diam. Outer bark c. 0.1 mm thick, black to brown, smooth, puberulent when young, glabrescent; inner bark 0.1–0.2 mm thick, dark reddish; wood white to yellow. Stipules elliptic, 1.5–2 by 0.5–1 mm, appressed pubescent, caducous. Leaves: petiole terete but grooved above, 0.8–4.5 mm long, 0.9–1.1 mm diam, often more or less appressed pubescent; blade elliptic, 9–16 by 4–7.5 cm, coriaceous to chartaceous, base acute to rounded, without glands, margin crenate, teeth glandular, apex acuminate to shortly caudate, upper surface brown to black (when dry), lower surface pale brown, both sides pubescent when young, glabrous when mature; midrib flat above, elevated beneath, nerves 7–9 pairs, veins reticulate, obscure above. Inflorescences: staminate ones axillary, peduncled; peduncles sometimes short and with few branches, 0.5–1.7 cm long, 1–1.5 mm diam, appressed pubescent; bracts elliptic, 1.5–3 by 0.5–1.2 mm, margin slightly ciliate, apex acuminate, appressed pubescent outside; pistillate inflorescences not seen. Staminate flowers c. 4 mm diam; pedicel c. 0.5 mm long, c. 0.3 mm diam, pubescent to puberulent; sepals 5, elliptic, 2–2.4 by 1–1.2 mm, base connate, margin entire, apex acute to acuminate, densely pubescent to puberulent outside; petals only 3 observed, but withered, elliptic, 1.4–1.6 by 0.7–1 mm, white, base connate, margin entire, apex acute, glabrous on both sides; disc lobes irregular, nearly semi-orbicular, 0.2–0.3 by c. 0.3 mm; stamens c. 9, arranged into 2 whorls, outer whorl 5, alternate with disc glands, opening introrse, free, filaments c. 0.15 mm long, inner whorl c. 4, opening more or less extrorse, connate into an androphore, hidden, c. 0.5 mm long, anthers ellipsoid, c. 0.6 mm long. Pistillate flowers, fruits and seeds unknown.

    Distribution — Philippines (endemic on Mindanao).

   « = Tritaxis cumingii; l = Trigonostemon angustifolius; n = Trig. stenophyllus; ▲ = Trig. whiteanus

    Habitat & Ecology — Rugged country, on red clay soil. Altitude: 300 m. Flowering: June.

    Note — A rare and poorly known species. The stamens are arranged into two whorls with c. 5 free outer and 4 inner connate ones, which seems typical for Tritaxis, but the inflorescences are too much condensed. These are perhaps still young and might grow into larger inflorescences as only buds are present. A molecular phylogenetic study is necessary to determine this species affiliation.

3. Tritaxis denticulata (Merr.) R.Y.Yu & Welzen

   Tritaxis denticulata (Merr.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 932. — Dimorphocalyx denticulatus Merr., Philipp. J. Sci. 4, Bot. (1909) 278; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iv (1912) 285; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 455; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 96; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20; Welzen & Oostrum, Blumea 53 (2015) 195, fig. 1b, d, e; map 2. — Syntypes: FB (Whitford & Hutchinson) 9033 (K, PNH lost, US), Philippines, Mindanao, District of Zamboanga, Port Banga.

   Dimorphocalyx murinus Elmer, Leafl. Philipp. Bot. 4 (1911) 1285 (‘murina’); Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 404; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 455; Whitmore, Tree Fl. Malaya 2 (1973) 87; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 97; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 21. — Lectotype (designated by Welzen & Oostrum, 2015): Elmer 12844 (holo L; iso BM, HBG, K, L, NY, P, U under D. lawianus, US), Philippines, Palawan, Puerto Princesa (Mt. Pulgar).

   Dimorphocalyx loheri Merr., Philipp. J. Sci. 27 (1925) 30; Enum. Philipp. Fl. Pl. 4 (1925) 252; Airy Shaw, Kew Bull. 20 (1920) 413; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20. — Lectotype (designated by Welzen & Oostrum, 2015): Loher 12467 (holo UC; iso A), Philippines, Luzon, Rizal Prov., Montalban.

(Under)shrubs to trees, to 20 m high, d.b.h. to 20 cm; flowering branches 1–2.5 mm thick, round, slightly striate, often strongly lenticellate, hairy when young, persistent at nodes. Indumentum of light yellow hairs, present on most parts. Outer bark green to pale white to greyish to grey-brown to light brown, smooth to deeply fissured to scaly, thin to 4 mm thick, soft (to hard); inner bark 0.3‒0.5 cm, pale yellowish to pink to red to red-brown to (pale) brown, fibrous, (soft to) hard; exudate red; sapwood creamy white and dull ochre, c. 2 cm thick; heartwood light red-brown. Stipules ovate, 3‒5 by 2.2‒3.8 mm, outside (glabrous to) hairy, glabrescent, inside glabrous. Leaves: petiole 2‒10 mm long (see note 2), 1–3.1 mm diam, completely pulvinate, usually slightly hairy; blade elliptic, widest in ± middle, 7.9–30 by 3.3–12 cm, 1.8–3.2 times as long as wide, rather coriaceous, base rounded to cuneate, margin serrulate to serrate, revolute, apex (acuminate to) cuspidate to caudate, upper surface seldom with few hairs, dull dark green, lower surface often with few hairs, light green to glaucous, venation slightly raised to slightly sunken above, raised below, secondary veins 8–17 pairs, intercalary veins present, tertiary nerves and veinlets reticulate. Inflorescences axillary, cymose to thyrsoid, usually short, to 5 cm long, round to flattened and angular, (sparsely) hairy; staminate flowers in groups per node, pistillate flowers single per node and often single per inflorescence; bracts in various shapes, very broad and short to long, narrow and sharply folded to leaf-like, triangular to ovate to elliptic, 1.8–8 by 1.3–4 mm, margins thinner, with lighter colour when dry, outside (very) hairy, inside glabrous. Staminate flowers 10–13 mm diam, white; pedicel to 10 mm long above basal abscission zone, round, (slightly) hairy; calyx lobes often unequal, 4.3–5 mm deep, lobes ovate, 2.4–3 by 1.9–2.6, apex slightly emarginate to rounded, outside (glabrous to) hairy, inside glabrous (to basally slightly hairy); petals oblong to obovate, 5.3–7.3 by 2.6–3.6 mm, usually outside slightly hairy, apex rounded; disc glands rather thick, zig-zagging around stamens, hairy; stamens 16–18, the outer ones with (nearly) free filaments of c. 2 mm long, the inner ones diverging in two layers from an up to 2 mm long androphore, free part of filaments c. 1.5 mm long, anthers c. 0.7 by 0.7 mm. Pistillate flowers 12–22 mm diam; pedicel c. 9 mm long, round, hairy; sepals connate at base, lobes enlarging directly after opening (see note 3), obovate, c. 8.2 by 4.2 mm, green, outside hairy, inside glabrous, apex rounded; petals elliptic to oblong, 4.8–9 by 3–6 mm, usually shorter than calyx lobes, white, hairy outside, glabrous inside, apex rounded; disc a flat ring, hairy, cream; ovary 2.5–4 by 2–4 mm, hairy (to perhaps seldom glabrous), glabrescent, green, stigmas 3–7 mm long of which upper 0.9–5 mm split, thick, broad, hairy below, green to yellow. Fruits 1.3–1.7 by 1–1.3 cm, smooth, hairy, glabrescent, green to slightly brownish green to greenish blue to purple, also cream mentioned; wall woody, 1–1.2 mm thick, exocarp often separating; pedicel elongating up to 25 mm; sepals enlarged to 12.8 by 5 mm (see note 3); columella 7–12 mm long. Seeds 8–12 by 6.5–10.5 by 5.5–9 mm.

    Distribution — Malay Peninsula (Johore), W and Central Borneo, Philippines.

    Habitat & Ecology — Mixed dipterocarp lowland forest to logged over areas on hillsides, ridges and along rivers; soil blackish sand to sandy clay to loam to sandstone shale; bedrock igneous intrusive. Altitude: sea level to  700 m. Flowering: March to November; fruiting: February, March, May to August, October to December.

    Vernacular names — Borneo: Kalimantan Barat: Buronte girek; Sabah: Alag alag, putat putat (Tidong); Binsuon, Parumpong (Dusun Kinabatangan). Philippines: Dagongdong, Pagang-dong (Tagbanua).

    Notes — 1. The type of D. denticulatus resembles the specimens of D. pauciflorus of Borneo. However, D. pauciflorus has echinate fruits, and the presence of spines on the ovary of D. denticulatus was not described by Merrill (1909). In habit the type of D. denticulatus resembles other Philippines specimens identified as D. murinus Elmer (serrulate leaf margin, short petioles). Therefore, the latter, younger name is synonymised with D. denticulatus.

    2. Dimorphocalyx loheri is tentatively placed in the synonymy here. Airy Shaw (1983) suggested ‘Genus uncertain, probably not Dimorphocalyx, but available material insufficient’. However, according to the description by Merrill (1925a; unfortunately flowering isotypes are absent and the holotype is lost) this species is more like D. murinus, because of the hairy floral parts, than D. denticulatus; names which are here considered as conspecific.

    3. SFN (Corner) 37248 from Johore, Malay Peninsula, has pistillate sepals that do not directly enlarge when the flower opens, similar to a specimen with unknown collector and origin (L, barcode L  0158646). The latter also has exceptionally long petioles (up to 16 mm long), but still has the typical D. murinus hairy disc.

4. Tritaxis ixoroides (C.B.Rob.) R.Y.Yu & Welzen

    Tritaxis ixoroides (C.B.Rob.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 932. — Ostodes ixoroides C.B.Rob., Philipp. J. Sci. 6, Bot. (1911) 332; Pax & K.Hoffm. in Engl., Pflanzenr. IV. 147.vii (1914) 403; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 454. — Dimorphocalyx ixoroides (C.B.Rob.) Airy Shaw, Kew Bull. 20 (1967) 412; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20; Welzen & Oostrum, Blumea 53 (2015) 196, map 3.  — Type: FB (Klemme) 13426 (holo PNH, lost; iso US), Philippines, Luzon, Province of Ilocos Norte, Bangui.

Small trees, to 6 m high, d.b.h. to 18 cm; flowering branches 1–3 mm thick, round to somewhat angled, brownish, striate. Indumentum mainly absent. Outer bark brownish or greyish, striate, c. 0.5 mm thick; inner bark light brownish; sapwood c. 0.5 mm thick; heartwood c. 1 cm thick. Stipules triangular, 1.7–3 by 1–1.2 mm, glabrous to slightly hairy outside, late caducous. Leaves: petiole 2–8 mm long, 1.2–3.2 mm diam, round, completely pulvinate, glabrous; blade narrowly ovate, widest near the base, 8.5–26 by 2–8.7 cm, 3–6 times as long as wide, base emarginate to cordate, margin serrulate, flat, with glands abaxially in the teeth, apex gradually, indistinctly cuspidate, venation slightly raised on both sides, secondary veins 15–20 pairs, with intercalary nerves present, tertiary and higher order nerves reticulate. Staminate inflorescences thyrsoid, to 15 cm long, slightly paniculate with few, short side-branches, round, glabrous, green; staminate flowers in cymose groups along side branches, pistillate inflorescences racemose, up to 11.5 cm long with a single flower per node; bracts varying between broad and ovate, c. 0.8 by 1 mm, to narrow and elliptic, c. 0.9 by 0.4 mm, hairy outside, especially the margin.. Staminate flowers seen in bud, 3.2–7 mm diam; bud of 3.2 mm diam described: pedicel c. 2 mm long above abscission zone, round, glabrous; calyx c. 3.2 mm high, glabrous to slightly hairy, especially the margin, lobes ovate, c. 2 by 1.8 mm, margin membranous, apices round, without subapical glands outside; petals free, broadly obovate, c. 2.7 by 1.8 mm (Robinson, 1911: c. 6 mm long), glabrous, apex round; disc glands triangular, 0.3–0.6 by c. 0.5 mm, glabrous; stamens c. 10, filaments strap-like, apically narrowed, outer ones 4, free, c. 1 mm long, inner 6 partly united in a c. 1 mm high androphore, free part c. 0.8 mm long, anthers to 1 mm long. Pistillate flowers c. 4 mm in diameter, pedicel c. 3 mm long above abscission zone, round, glabrous; sepals connate at base, lobes elliptic, c. 4.5 by 3 mm, glabrous, without subapical glands outside; petals ovate, c. 5 by 2 mm, glabrous; disc a flat ring, glabrous; ovary c. 2.5 by 2 mm, glabrous, stigmas c. 0.25 mm long. Fruits 1.6–1.8 by 1.3–1.5 cm, smooth, glabrous; sepals enlarged to 1 by 0.5 cm; pedicel c. 9 mm long; wall woody, c. 0.5 mm thick; columella c. 8 mm long. Seeds c. 8 by 6 mm.

    Distribution — Philippines (endemic on Luzon).

    «= T. ixoroides (l = T. muricata)

    Habitat & Ecology — On slopes in forest. Altitude: c. 435 m. Flowering: January, February, May, June, October, November; fruiting: January to March, May, June, December.

5. Tritaxis malayana (Hook.f.) R.Y.Yu & Welzen

    Tritaxis malayana (Hook.f.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933. — Dimorphocalyx malayanus Hook.f., Fl. Brit. Ind. 5 (1887) 404; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 33; Merr., J. Straits Branch Roy. Asiat. Soc., Special Number (1921) 346; Ridl., Fl. Malay Penins. 3 (1924) 266; W.L.Stern, Amer. J Bot. 54 (1967) 668; Whitmore, Tree Fl. Malaya 2 (1973) 86; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 96; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1 (2005) 229, fig. 50; Welzen & Oostrum, Blumea 53 (2015) 197, fig. 1f, map 4. — Lectotype (designated by Welzen & Oostrum, 2015): Griffith KD 4785 (holo K; iso A, P), [Malaysia,] Malacca.

    Dimorphocalyx kunstleri King ex Hook.f., Fl. Brit. Ind. 5 (1887) 405; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 32; Ridl., Fl. Malay Penins. 3 (1924) 266. — Type: King’s collector 1455 (holo K), [Malaysia,] Penang.

   Dimorphocalyx luzoniensis Merr., Philipp. J. Sc. 5, Bot. (1910) 192; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iv (1912) 284; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 455; Whitmore, Tree Fl. Malaya 2 (1973) 87; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 96; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 21. — Lectotype (designated by Welzen & Oostrum, 2015): FB (Tamesis) 11907 (holo K; iso US), Philippines, Luzon, Province of Laguna, Los Baños.

    Dimorphocalyx beccarii Gagnep., Bull. Soc. Bot. France 71 (1924) 621. —Lectotype (designated by Welzen & Oostrum, 2015): Beccari PB 2215 (holo P; iso A, K), Borneo, Sarawak.

   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; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20. —Type: Elmer 17296 (holo PNH, lost; iso HBG, K, L, MO, NY, S, U), Philippines, Luzon, Prov. of Sorsogon, Irosin (Mt. Bulusan).

Shrubs to trees, to 15 m high, d.b.h. to 18 cm; flowering branches 2–3 mm diam, greyish brown, yellowish when dry, at most slightly striate. Indumentum mainly absent, hairs light yellow. Outer bark grey, thin, slightly roughened, not detaching; under bark usually indistinct, if distinct dark red; inner bark cream to paler red than under bark, fibrous; wood white. Stipules triangular to ovate, 1–3 by 1–3 mm, stiff, with dark brown centre and thinner, lighter brown margins, glabrous. Leaves: petiole 7–35 mm long, 0.8–1.8 mm diam, deeply furrowed above, not to slightly pulvinate basally and apically, glabrous, light green to green; blade ovate to elliptic, widest in ± middle, 2.9–19 by 0.8–10.3 cm, 1.8–3.6 times as long as wide, papyraceous (to pergamentaceous), base obtuse to cuneate to attenuate, margin entire, seldom serrulate (glandular parts extending due to revolute margin), flat to revolute, apex (acuminate to) cuspidate (to caudate), dark green above, pale green below, venation slightly raised above, raised below, secondary veins 9–17 pairs, tertiary nerves reticulate. Inflorescences axillary, short and dichasial (especially pistillate ones) to longer and thyrsoid (to slightly paniculate; especially staminate ones), staminate ones to 10 cm long, pistillate to 7 cm long, branches often flattened, glabrous, lower bracts often leaf-like, higher ones triangular to ovate, 0.7–6 by 0.3–1.5 mm, with a few hairs on the midrib outside and along the margin. Staminate flowers 6.5–13 mm diam, white; pedicel 3.7–6.5 mm long above abscission zone, round, glabrous, abscission zone basally (Philippines, Borneo) to generally higher (SE Asia); calyx 2–5.5 mm deep, lobes triangular and indistinct in SE Asia (c. 1 by 2.5 mm) with acute to erose apices, sometimes with a subapical gland outside, ovate and distinct in Borneo and the Philippines (1.3–3.5 by 1.3–3.3 mm) with round apices without glands outside; petals elliptic to oblong, 5–7.5 by 1.8–3.8 mm, apex rounded, glabrous; disc glands obtrapezoid, 0.3–0.9 by 0.6–0.8 mm, thin, glabrous; stamens 10–12, filaments white, outer 5 (or 8) free (to seldom basally connate for c. 1 mm with androphore), filaments 2.5–5 mm long, inner 4–7 often in two layers, androphore 2.3–6 mm long, free part 1–2 mm long, anthers ellipsoid, 0.8–1.1 by 0.8–1.5 mm, tan. Pistillate flowers 20–21.5 mm diam; pedicel 5–12 mm long above abscission zone, round, glabrous; calyx basally united, lobes ovate to oblong to obovate, 8–13 by 5–7.5 mm, apex rounded to emarginate, glabrous, usually with a gland outside just beneath apex, green to yellow; petals elliptic to obovate, c. 9.5 by 4.5 mm, apex rounded, white, glabrous; disc up to 0.4 mm high, glabrous; ovary ovoid, 2–2.2 by 1.7–2.2 mm, glabrous, smooth, bright yellow with local green tinges, style 0.8–1 mm long, cream or very pale green, stigma 2–5 mm long, basal 1–1.3 not split. Fruits 1.2–1.6 by 0.9–1 cm, smooth, glabrous, green, ripe brown; pedicel 8–19 mm long; sepals enlarging to 25 by 16 mm; wall c. 1 mm thick, exocarp detaching; columella c. 8.5 mm long. Seeds ellipsoid, 7.5–8 by 6.5–7.5 by 6–6.8 mm.

    Distribution — Thailand (Peninsular), Malay Peninsula, Borneo, Philippines.

    Habitat & Ecology — In primary and lowland evergreen to deciduous forest, on slopes, sandstone cliffs, among limestone outcrops. Alt.: 100–500 m. Flowering: January to May, September; fruiting: February to June.

    Notes — Dimorphocalyx luzoniensis and D. bulusanensis do not differ in any characters from each other and both are also very similar to D. malayanus and, therefore, synonymised with the latter. There are some geographical differences: leaf blades are generally larger in Borneo and the Philippines (‘D. luzoniensis’, ‘D. bulusanensis’) than in S Thailand and Malay Peninsula (typical D. malayanus), staminate flowers of typical D. malayanus generally have a visible abscission zone, not basal, and they are smaller with acute, very short calyx lobes (basal abscission zone and larger, with bigger, rounded calyx lobes in typical ‘D. luzoniensis/bulusanensis’), the pistillate sepals in S Thailand and Malay Peninsula are generally more rounded/acute and always have a subapical extrafloral nectary at the outside, while on Borneo and in the Philippines the pistillate sepals are emarginate and often lack the glands, the style and disc are more distinct in S Thailand and Malay Peninsula than in the Philippines.

6. Tritaxis moluccensis (Welzen & Oostrum) R.Y.Yu & Welzen

    Tritaxis moluccensis (Welzen & Oostrum) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933. — Dimorphocalyx moluccensis Welzen & Oostrum, Blumea 53 (2015) 198, map 1. — Type: De Vogel 3134 (holo L), Indonesia, N Moluccas, Halmahera, Ekor, side of Gunung Panjang.

    Dimorphocalyx cf. muricatus auct. non (Hook.f.) Airy Shaw: Airy Shaw, Kew Bull. 37 (1982) 16.

Trees to 12 m high, d.b.h. to 28 cm, one specimen fluted, flutes c. 4 m high, c. 2 m out and c. 5 cm wide; flowering branches 2.5–3 mm thick, round, glabrous. Indumentum of light yellow hairs, most parts glabrous. Outer bark brownish grey, not fissured, c. 0.2 mm thick; inner bark red, c. 3 mm thick, without exudate; sapwood pale yellow tinged violet, gradually passing into the darker yellow heartwood. Stipules triangular, 4–4.5 by c. 3.5 mm, thick, margins thinner, outside glabrous to hairy, inside glabrous, caducous. Leaves: petiole 0.8–2 cm long, 1.5–3 mm diam, above flat to furrowed, glabrous to few hairs, completely pulvinate; lamina elliptic to oblong, widest in ± middle, 10.5–24.5 by 5.8–12.8 cm, 1.8–1.9 times as long as wide, (rather) coriaceous, base rounded to attenuate, margin laxly serrulate, with glands in the teeth abaxially, recurved, apex acute to acuminate, mainly glabrous, venation slightly raised above and beneath, secondary veins 13–15 pairs, higher order veins reticulate. Staminate inflorescences terminal and axillary on apical nodes, several close together, thyrsoid to slightly paniculate with short side branches, to 11.3 cm long, angular to flattened, hairy, quickly glabrescent; bracts ovate, 2.7–4 by 1.7–3 mm to elliptic, c. 5 by 1 mm, outside usually hairy, inside glabrous. Staminate flowers c. 8 mm diam, white, unpleasant smell; pedicel 4.5–5.5 mm long above abscission zone, round to slightly flattened, with few hairs, abscission zone well-visible, not hidden by bracts; calyx 3–3.3 mm high, lobes ovate, 1.7–2.3 by 2–2.5 mm, thickest in middle, thinnest at margins, margin and often base outside hairy, apex emarginate to rounded; petals ovate to obovate, 4.2–5.5 by 3.3–6 mm, apex rounded, few hairs outside; disc glands rectangular (not zig-zagging around stamens), 0.3–1 by 0.3–0.8 mm, thick, apex hairy; stamens 11–12, 5 outer free or base adnate to androphore, filaments c. 4.5 mm long, central 6 or 7 partly united in an androphore of c. 4 mm long, free part of filaments c. 1.5 mm, anther elliptic, 0.6–1 by 0.8–1 mm. Pistillate flowers, fruits and seeds unknown.

    Distribution — Endemic in the N Moluccas (Bacan, Halmahera).

« = T. moluccensis (l = T. australiensis; u = T. pauciflora; n = T. trichocarpa)

    Habitat & Ecology — Rather dense primary forest to secondary forest on deep clayey soil. Altitude: sea level to 15 m. Flowering: August, September.

7. Tritaxis muricata (Hook.f.) R.Y.Yu & Welzen

    Tritaxis muricata (Hook.f.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933. — Ostodes muricata Hook.f., Fl. Brit. Ind. 5 (1887) 401; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 21; Ridl., Fl. Malay Penins. 3 (1924) 269. — Ostodes muricata Hook.f. var. genuina Pax in Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 21, nom. inval. — Dimorphocalyx muricatus (Hook.f.) Airy Shaw, Kew Bull. 20 (1967) 412; Kew Bull. 26 (1972) 252; Whitmore, Tree Fl. Malaya 2 (1973) 87; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 97; Kew Bull. 36 (1981) 286; Phattar. & Chayam. in Chayam. & Welzen, Fl. Thailand 8, 1 (2005) 231, fig. 51, plate XIII: 1; Welzen & Oostrum, Blumea 53 (2015) 198, fig. 1g, map 3. — Type: King’s collector 3162 (holo K), [Malaysia,] Perak, Larut.

    Trigonostemon asahanensis Croizat, J. Arnold Arbor. 23 (1942) 54. — Type: Rahmat Si Boeea 9872 (holo A; iso L), Sumatra, Asahan, vicinity of Tomoean Dolok.

    Dimorphocalyx [!] sp.?, Merr., Pl. Elmer. Born. (1929) 163. — pro Elmer 21287 (L), British North Borneo [= Sabah], Elphinstone Province, Tawao.

    Ostodes muricata Hook.f. var. ? minor Hook.f., Fl. Brit. Ind. 5 (1887) 401. — Dimorphocalyx muricatus (Hook.f.) Airy Shaw var. minor (Hook.f.) Airy Shaw, Kew Bull. 20 (1967) 412; Whitmore, Tree Fl. Malaya 2 (1973) 87. — Lectotype (designated by Welzen & Oostrum, 2015): Lobb 304 (holo BM; iso E, GH, 2 sheets, K, L), Singapore.

Small shrubs to trees, to 10(–25) m high, d.b.h. to 18 cm, evergreen but seemingly deciduous in S Thailand, young leaves when flowering; flowering branches 2–5.5 mm thick, ± angular, light grey (to brown) when dry, striate when dry, smooth to lenticellate, mainly glabrous. Indumentum variably present. Outer bark grey to brown, smooth (to scaly and hooped), soft, papery, c. 0.2 mm thick; inner bark yellow to orange-red to red, soft, (laminated, fibrous), c. 2 mm thick; exudate watery, red; sapwood creamy white to pale yellow. Stipules triangular, 5–8 by 3–4 mm, glabrous to hairy outside, early caducous. Leaves: petiole (1.1–)3–14 cm long, (0.8–)1–4 mm diam, deeply furrowed above, glabrous to hairy, basally and apically slightly pulvinate; blade (ovate to) elliptic to oblong (to obovate), widest in ± middle, 6.8–42 by 2.6–13.2 cm, 1.9–3.7 times as long as wide, papyraceous to pergamentaceous (to coriaceous), base round to obtuse to cuneate, margin serrate (to serrulate), flat to revolute, with glands abaxially in the teeth, apex acuminate to usually cuspidate, upper surface dark green, at most hairy on midrib, lower surface pale green to blue-green, sometimes a bit hairy on venation, latter flat to slightly raised above, raised below, secondary veins 12–15 pairs, intercalary nerves often present, tertiary nerves scalariform, higher orders reticulate. Inflorescences axillary thyrses, to c. 19 cm long, but usually less than 5 cm long, staminate ones more or less paniculate with a few side-branches, pistillate ones often almost umbellate or dichasial, glabrous to usually shortly sericeous; staminate flowers several per node, pistillate ones single; bracts ovate (to elliptic), 1.5–4 by 1.2–2 mm, usually hairy outside, glabrous inside. Flowers: calyx lobes mostly hairy outside except for lobe margins, glabrous inside, usually with a large, round gland outside, often indistinct. Staminate flowers 14–15 mm diam, white, scented; pedicel 15–17 mm long above abscission zone, roundish to flattened, usually hairy; calyx 5–5.5 mm high, lobes ovate to elliptic, 3–3.5 by 2–4 mm, apex round; petals oblong to obovate, 8–12 by 2.8–4.5 mm, reflexed, glabrous, apex round; disc glands often indistinct, winding around stamens, glabrous; stamens 10–16, not in distinct whorls, only inner c. 3 with connate filaments, latter 3.5–4 mm long, anthers dorsifixed, 1.2–1.4 by 1–1.3 mm, inner ones largest. Pistillate flowers c. 8 mm in diam, not strongly scented; pedicel 6–13 mm long above abscission zone, round, hairy; sepals shortly connate, basally white, rest light green, lobes ovate to elliptic 3–6 by 3–4.5 mm, apex rounded; petals oblong to obovate, c. 8 by 6.2–7 mm, white, apex round; disc a thin ring, glabrous; ovary ovoid, 3.5–4.5 by 2–3 mm, densely beset with blunt spines, glabrous, style absent, stigmas 2–3.7 mm long, white to light green, completely split except for lower 0.5–1 mm, upper surface stigmatic. Fruits 1.8–3.5 by 1.5–2.7 cm, muricate with spines often united into short ledges, dark green to pink-yellow to brown, wall woody, c. 2 mm thick, exocarp and endocarp usually completely separating; pedicel elongated up to 24 mm; sepals slightly enlarged to 8 by 5 mm; columella 10.5-13 mm long. Seeds sub-ellipsoid with usually abaxially a lengthwise ridge, 8–14 by 6–11 by 7–10.5 mm.

    Distribution — Thailand (Peninsular: Narathiwat Prov.), Malay Peninsula, Sumatra, Borneo.

    l = T. muricata («= T. ixoroides)

    Habitat & Ecology — Evergreen forest, primary and (logged) secondary (Dipterocarp) forest, often on ridges and along rivers and swamps; soil varying from yellow clay to sandy clay to sandstone with clay to loam. Alt.: sea level up to 1000 m. Flowering: March to October; fruiting: whole year through.

    Vernacular names — Sumatra: Batin batin delok alafai, Batin batin silafai; Kajoe si saram. Borneo: Brunei: Asah anak unyong; Kalimantan: Kupang parawa (Dayak); Sarawak: Bantas (Iban); Marok (Kayan)).

8. Tritaxis pauciflora (Merr.) R.Y.Yu & Welzen

    Tritaxis pauciflora (Merr.) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933. — Ostodes pauciflorus Merr., Philipp. J. Sci. 11, Bot. (1916) 72; J. Straits Branch Roy. Asiat. Soc., Special Number (1921) 345. — Dimorphocalyx pauciflorus (Merr.) Airy Shaw, Kew Bull. 20 (1967) 413; Welzen & Oostrum, Blumea 53 (2015) 199, fig. 1a, h; map 1. — Syntypes: Hose 244 (A, K, L, P), Malaysia, Sarawak, Baram District, Baram.

Shrubs to treelets, to 8 m high, d.b.h. to 8 cm; young twigs greenish grey; flowering braches 1.5–2 mm thick, round, yellowish brown when dry, smooth. Indumentum of yellowish hairs most parts mainly glabrous. Outer bark grey to grey-brown, smooth. Stipules triangular, 1.8–3 by 1.8–2.5 mm, margin with few hairs, thick but margins thinner. Leaves: petiole 2.5–7 mm long, 0.8–1.7 mm diam, deeply grooved above, completely pulvinate, glabrous; blade slightly ovate to elliptic to slightly obovate, widest in ± middle, 12.3–21.4 by 2.8–5.7 cm, 2.4–4 times as long as wide, pergamentaceous to slightly coriaceous, base cuneate, margin serrulate, with glands abaxially in the teeth, recurved, apex (acuminate to) cuspidate, lower surface bluish green, venation slightly raised above, raised below, secondary veins 10–14 pairs, intercalary nerves mainly absent, higher order nerves reticulate. Inflorescences axillary, cymose, less than 1 cm long, square, slightly hairy; staminate flowers with few together, pistillate ones single; bracts triangular to ovate, c. 1.5–2 by 1–1.8 mm, margin hairy to slightly hairy outside. Staminate flowers only seen in bud; pedicel c. 20.5 mm long above abscission zone, round, glabrous; calyx c. 4.8 mm deep, lobes ovate, outside and inside glabrous, on each lobe a round gland near apex outside; petals oblong; stamens c. 20, anthers dorsifixed, c. 1 by 1 mm. Pistillate flowers c. 9.5 mm diam; pedicel c. 13.5 mm long above abscission zone, round to ribbed, glabrous; calyx c. 4.7 mm deep, lobes ovate, c. 4.3 by 3.7 mm, glabrous, on each lobe a round gland near apex outside; petals not seen; ovary ovoid, c. 5 by 3.5 mm, echinate with stump, apically slightly thickened soft spines, glabrous, stigmas not seen. Fruits outside with soft non-confluent spines, glabrous, ripe purple or red; calyx lobes hardly enlarged, 4–5 by 3.8–4 mm; wall woody, c. 1.2 mm thick, exocarp detaching or not; columella 9–10 mm long. Seeds c. 9 by 8 by 7 mm.

    Distribution — Endemic in W Borneo (Brunei, Sarawak).

u = T. pauciflora (l = T. australiensis; « = T. moluccensis; n = T. trichocarpa)

    Habitat & Ecology — Primary lowland dipterocarp forest to secondary forest, usually on hill slopes and ridges; soil: sandy clay to sandstone and shale. Altitude: 20–400 m. Flowering: April, May, August, September; fruiting: January, April, June, August to October.

    Uses  — Roots are boiled together with roots of Psychotria cf. crassifolia Miq. (Rubiaceae), mixture is drunk and known as the medicine ‘Ubat sara’.

    Note — This species, formerly united with D. denticulatus, is here reinstated. It only occurs locally in NW Borneo and differs from the typical D. denticulatus). Typical are the ecahinate fruits and the sepals that are only slightly hairy along the margin and generally show a round glandular thickening on every sepal lobe.

9. Tritaxis trichocarpa (Airy Shaw) R.Y.Yu & Welzen

    Tritaxis trichocarpa (Airy Shaw) R.Y.Yu & Welzen in R.Y.Yu et al., Taxon 68 (2019) 933. — Dimorphocalyx luzoniensis Merr. var. trichocarpus Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 96. — Dimorphocalyx trichocarpus (Airy Shaw) Welzen & Oostrum, Blumea 53 (2015) 199, map 1. — Type: S (Anderson) 20974 (holo K; iso L), Malaysia, Sarawak, First Division, Bidi, Bau.

Trees, d.b.h. to 12 cm; flowering branches 3–4.5 mm diam, yellowish when dry, slightly lenticellate. Indumentum of light yellow hairs. Outer bark grey, smooth. Stipules caducous, base at least 4.5 mm wide, slightly hairy outside, especially in the thicker centre, stiff. Leaves: petiole 25–36 mm long, 1.2–3 mm diam, deeply furrowed to flattened above, slightly pulvinate basally and apically, glabrous; blade slightly ovate to slightly obovate, widest in ± middle, 22–33 by 9.4–14.3 cm, c. 2.3 times as long as wide, papyraceous, base rounded, margin laxly serrulate, with glands abaxially in the teeth, recurved, apex acuminate, venation flat to slightly sunken above, raised below, secondary veins 13–16 pairs, higher order nerves reticulate. Staminate inflorescences and flowers not seen. Pistillate inflorescences axillary, short, racemose, one flower developing into fruit; flattened to angular, hairy; most bracts broken, one leaf-like, c. 12 by 7 mm, others ovate, c. 6 by 4 mm, outside hairy, inside glabrous. Young fruits smooth, densely hairy, green; pedicel c. 24 mm long above abscission zone, hairy; sepals enlarging, unequal, 14–17.5 by 11–15 mm, glandless, outside and inside hairy; petals caducous; disc glabrous; style c. 1 mm long, densely hairy, stigmas c. 5 mm long, basal 1.5 mm not split, hairy beneath. Seeds not seen.

    Distribution — Borneo (endemic in Sarawak).

n = T. trichocarpa (l = T. australiensis; « = T. moluccensis; u = T. pauciflora)

    Habitat & Ecology — At base of limestone hill on limestone rocks with intervening igneous derived soil. Altitude: c. 100 m. Fruiting: April.

    Note — Only known from the type, which is very distinct by its very large leaves, rather long petioles, hairy, enlarging sepals, hairy fruits and glabrous discs. Because of its distinctiveness this taxon is raised to species level.

DUBIOUS NAME

   Dimorphocalyx angustifolius (Merr.) Airy Shaw, Kew Bull. 20 (1967) 412; Alphab. Enum. Euphorb. Philipp. Isl. (1983) 20; Welzen & Oostrum, Blumea 53 (2015) 199. — Ostodes angustifolia Merr., Philipp. J. Sci. 7, Bot. (1912) 403; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 414; Merr., Enum. Philipp. Fl. Pl. 2 (1923) 454. — Type: FB (Whitford & Hutchinson) 9343 (?), Philippines, Mindanao, district of Zamboanga, Port Banga.

    Note — Typical for this taxon are the very long, linear-lanceolate leaves (18–27 by 1–1.5 cm). Unfortunately, the type was probably lost during the second world war and the original description also contains no indication of characters typical for Dimorphocalyx.

EXCLUDED TAXA

   Dimorphocalyx (?) borneensis Merr., Philipp. J. Sci. 11, Bot. (1916) 73; J. Straits Branch Roy. Asiat. Soc., Special Number (1921) 345; Welzen & Oostrum, Blumea 53 (2015) 199. — Trigonostemon merrillianus Airy Shaw, Kew Bull. 25 (1971) 549, non Trigonostemon borneensis Merr. — Type: Hose 420 (iso A, K, L), Malaysia, Sarawak, Baram District, Entoyut River. = Trigonostemon villosus Hook.f. var. merrillianus (Airy Shaw) R.Y.Yu & Welzen.

   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; Welzen & Oostrum, Blumea 53 (2015) 199. — Type: Lobb s.n. (holo K), Singapore. = Trigonostemon capillipes (Hook.f.) Airy Shaw (Kew Bull. 20, 1967, 412).

   Dimorphocalyx longipes Merr., Philipp. J. Sc. 1, Suppl. (1906) 82; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 33Welzen & Oostrum, Blumea 53 (2015) 200. — Syntypes: FB (Borden) 1801 (NY, US), FB (Whitford) 1066 (NY, P, US), Philippines, Luzon, Bataan Prov., Lamao; Merrill 2699 (US), Philippines, Luzon, Prov. of Rizal, Bosoboso. = Trigonostemon longipes (Merr.) Merr. (Philipp. J. Sci. 11, Bot, 1916b, 191).

   Dimorphocalyx ovalis Ridl., J. Straits Branch Roy. Asiat. Soc. 59 (1911) 178; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.vii (1914) 404; Welzen & Oostrum, Blumea 53 (2015) 200. — Syntypes: Curtis s.n. (not seen), Malaysia, Lan(g)kawi, Kwah/Coah; Ridley 14890 (not seen), Malaysia, Perlis, Bukit Telor Jambu, Kanga/Kanya. = Actephila ovalis (Ridl.) Gage (Rec. Bot. Surv. India 9 (1922) 219).