Flora of Thailand
Euphorbiaceae
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Hook.f., Hook. Icon. Pl. 16: t. 1592. 1887; Fl. Br. Ind. 5.: 466. 1888; Croizat, J. Arnold Arbor. 22: 425. 1941; Airy Shaw, Kew Bull. 23: 119. 1969; Kew Bull. 26: 309. 1972; Whitmore, Tree Fl. Mal. 2: 117. 1973; Airy Shaw, Kew Bull. Add. Ser. 4: 175. 1975; Kew Bull. 36: 330. 1981; G.L.Webster, Ann. Missouri Bot. Gard. 81: 94. 1994; Radcl.-Sm., Gen. Euphorbiacearum: 251. 2001; Phuphat. in Welzen & Chayam., Fl. Thailand 8, 2: 442. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 153. 2014. Clavistylus J. J. Sm. ex Koord & Valeton, Meded. Dept. Landb. Ned.-Indiλ 10: 517. 1910.
Twining vines, monoecious or dioecious. Indumentum of stinging, silvery hairs and simple hairs, plants pubescent to glabrescent. Stipules triangular, persistent. Leaves alternate, simple, petiolate, eglandular; blades symmetric, papery, base cordate, rounded, obtuse or cuneate, not to distinctly peltate, margin subentire to serrulate, rarely dentate apically, venation 3-nerved to palmate. Inflorescences racemes, axillary, unisexual or bisexual with 1 or 2 basal pistillate flowers; flowers single per node, each subtended by a bract and 2 bracteoles; bracts and bracteoles elliptic, persistent. Flowers unisexual, actinomorphic, pedicillate; petals and disc absent. Staminate flowers: calyx-tube bowl- or cup-shaped, often contracted at mouth, with rim thickened and/or inflexed, disc-like, lobes 3, valvate, ovate; stamens 3, free, inserted in centre of calyx tube, filaments thick, anthers introrse, 2-locular, connective thickened, triangular, usually lacking or sometimes with an appendage; pistillode absent. Pistillate flowers: sepals 3 or 6; ovary 3-locular, 1 ovule per locule, 3-lobed, covered in stinging hairs; styles partly connate into a globose to obconic structure, obscurely to distinctly three-lobed at apex, lobes spreading or not. Fruits dehiscing capsules, 3-lobed, thin-walled, dehiscing into 3 2-valved cocci; sepals enlarged and persistent. Seeds subglobose, ecarunculate.
A genus of 5 species of southeast Asia and Malesia; one species in Thailand. Classification: Subfam. Acalyphoideae, tribe Plukenetieae, subtribe Tragiinae.
Megistostigma burmanicum (Kurz) Airy Shaw, Kew Bull. 23: 119. 1969; Airy Shaw, Kew Bull. 26: 309. 1972; Whitmore, Tree Fl. Mal. 2: 84, 117. 1973; Phuphat. in Welzen & Chayam., Fl. Thailand 8, 2: 442, Fig. 41, Plate XXIII: 1. 2007. Tragia burmanica Kurz, J. Asiat. Soc. Bengal, Pt. 2, Nat. Hist. 42: 244. 1873; For. Fl. Brit. Burma 2: 398. 1877; Hook.f., Fl. Brit. Ind. 5: 466. 1888; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 99. 1919.
Vine, monoecious, basal diameter up to 20 mm; stems twining, 1-3.5 mm in diameter, appressed-pubescent. Bark thin, smooth, tan. Stipules 1.5-8 by c. 3 mm. Leaves: petiole 3-11 cm long, sparsely to moderately pubescent; blade broadly ovate, 7-19 by 5-14 cm, length/width ratio 1.1-1.4(-2), chartaceous, base cordate with sinus 1-3.5 cm deep, margin subentire to remotely serrulate, apex acuminate to caudate, with tip 1-2 cm long, both sides sparsely pubescent, dull dark green above, pale light green underneath; nerves 3-5 per side. Inflorescences racemes, up to 4 cm long, axes appressed-pubescent; staminate bracts 1-3 mm long, pistillate bracts 2.5-4 mm long. Staminate flowers 8-9 mm in diameter when open; pedicel 1-1.3 mm long; calyx light yellowish, tube bowl-shaped, 1.8-2 by 0.8-1 mm deep; lobes broadly ovate, 3-4 by 2.5-4.5 mm, sparsely appressed hairy outside, few short thick papillae inside, apex obtuse; stamens c 1.3 by 1.3-1.4 mm, abruptly narrowed at base; anthers c. 0.3 by 1.3-1.4 mm, red-brown; the two anther sacs divergent, the connective extended as a blunt appendage directed inward. Pistillate flowers: pedicel c. 0.7 mm long; sepals 6, narrowly ovate, 3.4-9 by 1.8-4 mm, with dense cover of stinging hairs on both sides, light green; ovary c. 3-4 by 3.5-4 mm; styles mostly connate into an obconic structure, c. 4 by 4 mm, sparsely pubescent, 3-lobed at apex, with glabrous stigmatic surface, light green. Fruits 3-lobed capsules, c. 16 by 7-9 mm, dark brown, covered in course brown stinging hairs, on peduncle 2-6 cm long; sepals 12-18 by 6-10 mm, persistent, moderately covered in stinging hairs. Seeds subglobose, 5.7-6 by 5.4-5.8 by 5.4-6 mm, coursely mottled cream and brown.
Thailand. NORTHERN: Chiang Mai (Doi Chiang Dao, Doi Suthep-Pui National Park, Samong), Lampang (Doi Kuhn Dahn National Park, Jae Sawn National Park, Nahng Kaht Cave), Nan (Ban Nan Dun); South-western: Kanchanaburi (Klang Dong, Sisiwat); Peninsular: Satun (Satun).
Distribution. Burma (type), Thailand, Malay Peninsula.
Ecology. (Open margin of) evergreen forest, scrub, often in disturbed or open, fire-prone areas; soils: recorded on alluvial soil; bedrock granite, limestone or shale. Altitude: 1001,425 m.
Vernacular. Han taen (หานแตน), Han salit (หานสลิด) (Chiang Mai).