Flora of Thailand
Euphorbiaceae
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L., Sp. Pl. 1192. 1753. Müll.Arg. in DC., Prodr. 15, 2: 768. 1866. Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 12. t. 4. 1919; Airy Shaw, Kew Bull. 26: 327. 1972; Whitmore, Tree Fl. Malaya 2: 84, 126. 1973; Gillespie, Syst. Bot. 18: 575. 1993; Webster, Ann. Missouri Bot. Gard. 81: 93. 1994; Radcl.-Sm., Gen. Euphorbiacearum: 247. 2001; Gillespie & S.S.Larsen in Welzen & Chayam., Fl. Thailand 8, 2: 509. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 148. 2014.— Pterococcus Hassk., Flora 25 (2), Beibl. 3: 41. 1842, nom. cons.; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 21. t. 7. 1919.— Hedraiostylus Hassk., Tidjdschr. Natuurl. Gesch. Physiol. 10: 141. 1842.— Sajorium Endl., Gen. Pl. suppl. 3: 98. 1843.— Angostylidium (Müll.Arg.) Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 17. t. 5. 1919.— Tetracarpidium Pax in Engl., Bot. Jahrb. Syst. 26: 329. 1899.— Pseudotragia Pax, Bull. Herb. Boissier, Sér 28: 635. 1908.
Twining vines or lianas, monoecious or rarely dioecious. Indumentum of simple (non-stinging) hairs, plants pubescent or glabrescent. Stipules small, triangular, caducous. Leaves alternate, simple, petiolate; blades symmetric, papery, margin subentire to serrulate, apex acuminate to cuspidate, venation pinnate to weakly palmate, veins usually scalariform, veinlets reticulate, with one to several pair(s) of flat glands present near base and and sometimes a pair of stipellae or a single knob-like structure at the insertion on the upper surface, sometimes with smaller flat glands scattered on lower surface (only neotropical species). Inflorescences solitary, racemes or racemose thyrses, axillary or terminal on short shoots, bisexual with pistillate flower(s) basal, 1(-10), or rarely unisexual, staminate flowers single per node or several per node in condensed or rarely open cymules, pistillate flowers single per node; bracts small, triangular, eglandular or rarely biglandular. Flowers actinomorphic, pedicellate; petals absent. Staminate flowers: sepals 4 or 5, valvate, opening wide at anthesis; disc segmented or annular, interstaminal, often reduced or absent; stamens 8-40, free, on convex, subglobose or elongate receptacle, filaments short to elongate or anthers sessile, anthers 4-locular, basifixed; pistillode absent. Pistillate flowers: sepals 4; disc absent; ovary 4-locular, 1 ovule per locule, 4-angled to deeply 4-lobed, with lobes tuberculate, carinate, or horned; styles partly to entirely connate, column cylindrical to globose or obovoid. Fruits loculicidally dehiscing capsules or indehiscent berries, deeply 4-lobed to subglobose, each carpel carinate or with central tubercle or wing. Seeds lenticular and laterally compressed, subglobose, or ovoid, ecarunculate.
Pantropical genus of 19 species; only one species in Asia and Thailand. This species and two African species (P. africana and P. hastata) are sometimes treated as the separate genus Pterococcus (Backer and Bakhuizen van den Brink 1963, Whitmore 1973, Airy Shaw 1972, 1975), but are more recently included within Plukenetia (Gillespie 1993, Webster 1994, Radcliffe-Smith 2001). Classification: Subfam. Acalphoideae, tribe Plukenetieae, subtribe Plukenetiinae.
Plukenetia corniculata Sm., Nova Acta Regiae Soc. Sci. Upsal. 6: 4. 1799. Croizat, J. Arnold Arbor. 22: 425. 1941; Gillespie & S.S.Larsen in Welzen & Chayam., Fl. Thailand 8, 2: 510, Fig. 66. 2007.— Hedraiostylus corniculatus (Sm.) Hassk., Cat. Hort. Bogor Alt. 234. 1844.— Sajorium corniculatum (Sm.) Dietr., Synops. Pl. 5: 331. 1852.— Pterococcus corniculatus (Sm.) Pax & K. Hoffm., Pflanzenr, IV.147.ix: 22. 1919; Backer & Bakh., Fl. Java 1:490. 1963; Airy Shaw, Kew Bull. 26: 327. 1972; Kew Bull. Add. Ser. 4: 187. 1975; Whitmore, Tree Fl. Malaya 2: 84, 126. 1973.— Pterococcus glaberrimus Hassk., Flora 25, Beibl.: 41. 1842; Ridl., Fl. Mal. Pen. 3: 309. 1924.
Vine, monoecious; stems twining, becoming woody. Stipules 1.2-2 by 0.5-0.8 mm. Leaves: petiole 3-9 cm long, moderately or sparsely pubescent; blade ovate, oblong-ovate, or sometimes elliptic, 6-16 by 3-11 cm, length/width ratio 1.4-2, thin chartaceous, base cordate with U-shaped sinus 0.5-2 cm deep, margin serrulate or serrate, very sparsely pubescent or glabrescent, major veins usually sparsely or moderately pubescent above, adaxially with 2 stipellae at insertion and 2 glands along margin 1-4 mm from insertion, stipellae ca. 0.5-1 mm long, usually curved; glands flat, circular or elliptic, 0.5-1 mm in diameter; venation weakly palmate, nerves 2-4 per side. Inflorescences racemes, terminal appearing, leaf-opposed or sometimes on short shoots, or rarely axillary, 1.5-5 cm long, bisexual with a single pistillate flower at the basal node, staminate flowers one or rarely two per node, flowers subtended by a bract and 2 very small braceoles, staminate bracts narrowly triangular, 0.5-1 mm long. Staminate flowers 1.5-2.3 mm in diameter when open, very sparsely pubescent to glabrescent; pedicel 1.3-2.5 mm long; sepals 4, ovate or elliptic, ca. 1 by 0.6 mm, apex acute; disc absent; androecium 0.4-0.6 by 0.6-0.8 mm, stamens 8-14 on small globose or convex receptacle, filaments conical, < 0.1 mm long. Pistillate flowers sparsely pubescent to glabrescent; pedicel 1.5-9 mm long, elongating to 2-5 cm in fruit; sepals narrowly triangular or elliptic, 1.2-2.2 by 0.5-1 mm; ovary -2.5 mm in diameter, 4-winged, wings rounded, laterally compressed, 0.5-2 mm long, elongating to 13 mm in immature fruit; styles completely connate into a depressed-globose column, 0.5-0.7 by 0.8-1.1 mm, glabrous, with cross-shaped stigmatic surface. Fruits 4-lobed capsules, 7-11 by 15-20 mm, surface irregularly verrucate, glabrescent, each lobe with a central strap-shaped wing, 6-12 by 2-3 mm. Seeds broadly lenticular, 8-11 by 6.5-8 by 5-6.5 mm, laterally compressed, obtuse-triangular in outline, with a radial keel, 0.3-0.7 mm wide, cream, pale orange-brown or brown with darker orange or brown irregular markings.
Thailand.— NORTHERN: Phitsanulok (Tung Salaeng Luang); SOUTH-WESTERN: Trat (Ko Chang).
Distribution.— From N. India to Thailand and throughout Malesia to Sulawesi and the Philippines.
Ecology.— Evergreen forests, in clearings or along trails. Altitude: 50-550 m.