Flora of Thailand
Euphorbiaceae
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Pax & K.Hoffm. in Engl. Pflanzenr. IV.147.ix: 108. 1919; Pax & K.Hoffm in Engl. & Harms, Pflanzenfam. ed. 2, 19e: 148. 1931; Airy Shaw, Kew Bull. 23: 115. 1969; Kew Bull. 26: 311. 1972; G.L.Webster, Ann. Missouri Bot. Gard. 81: 95. 1994; Radcl.-Sm., Gen. Euphorbiacearum: 260. 2001; Gillespie in Welzen & Chayam., Fl. Thailand 8, 2: 463. 2007; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 152. 2014.
Twining vines, monoecious. Indumentum of stinging hairs and simple hairs, plants pubescent to glabrescent. Stipules triangular, persistent. Leaves alternate, simple, petiolate, eglandular; blades symmetric to somewhat asymmetric at base, papery, base cordate, margin serrulate to serrate, sometimes lobed in apical half, apex acuminate, venation 3-nerved to weakly palmate. Inflorescences racemes, terminal on short shoots or appearing leaf-opposed, bisexual with 1-5 pistillate flowers basally; flowers single per node, each subtended by a bract and 2 bracteoles; bracts and bracteoles narrowly elliptic, persistent. Flowers very small, actinomorphic, pedicillate; petals absent. Staminate flowers: calyx lobes 4(-6), valvate, opening horizontally or somewhat reflexed at anthesis; disc annular, sometimes obscure; anthers 2(3), subsessile, inserted in central depression within disc; pistillode absent. Pistillate flowers: sepals 6(-8), persistent in fruit; disc absent; ovary 3-locular, 3-lobed, densely covered in stinging hairs, 1 ovule per locule; styles partly connate into a stout cylindrical to subglobose column, stigmas free, not bifid, strongly recurved. Fruits schizocarpus capsules, 3-lobed, thin-walled, dehiscing into 3 2-valved cocci. Seeds subglobose, ecarunculate.
A monotypic genus of tropical Asia, known from India and China (Hainan) to Indonesia and the Philippines. The genus is closely related to and possibly not distinct from the large and morphologically diverse genus Tragia. Classification: Subfam. Acalyphoideae, tribe Plukenetieae, subtribe Tragiinae.
Pachystylidium hirsutum (Blume) Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 108. 1919; Backer & Bakh.f., Fl. Java 1: 491. 1963; Gillespie in Welzen & Chayam., Fl. Thailand 8, 2: 465, Fig. 50. 2007.— Tragia hirsuta Blume., Bijdr. 630. 1825. Müll.Arg. in DC., Prodr. 15, 2: 937. 1866.— Tragia irritans Merr., Philipp. J. Sci., Bot. 9: 491. 1914.— Tragia hirsuta Blume var. irritans (Merr.) Merr., Enum. Philipp. Fl. Pl. 2: 446. 1923.— Pachystylidium hirstum (Blume) Pax & K.Hoffm. var. irritans (Merr.) Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.ix: 108. 1919.— Tragia gagei Haines, J. Proc. Asiat. Soc. Bengal, n.s. 15: 317. 1920.— Tragia delpyana Gagnep., Bull. Soc. Bot. France 71: 1027. 1924; in Lecomte, Fl. Indo-Chine 5: 393. 1926; Croizat, J. Arnold Arbor. 22: 425. 1941.
Vine, with long, slender, twining stems from woody rootstock; stems 1.5-3.5 mm in diameter, often drying dark reddish brown, sparsely to moderately hirsute. Stipules 1.6-4 by 0.5-2 mm, reddish-brown. Leaves: petiole 0.8-3(-5) cm long, sparsely to densely hirsute; blade oblong-ovate to oblong-obovate, 4.5-10(-) by 2-6(-10) cm, length/width ratio 1.3-2.8, base cordate with sinus 0.2-2 cm deep, chartaceous, sparsely hirsute to glabrescent with midrib often hirsute and short pubesent, margin remotely serrulate to coursely serrate, sometimes subentire, coursely rounded-dentate, or irregularly lobed with 1-2 small lobes in apical half (only in Thailand), acumen 0.4-1 cm long; nerves 3-5 per side. Inflorescences narrow, 1-8 cm long, axes sparsely to densely hirsute and short pubescent; bracts 1.2-2.2 mm long, drying reddish brown. Staminate flowers pale green, 2-3 mm in diameter when open, greenish; pedicel 1-2.3 mm long; calyx lobes ovate, 0.9-1.3 by 0.5-1 mm, sparsely to moderately pubescent, apex acute; disc 0.8-1.3 mm in diam.; androecium 0.4-0.8 mm wide, anthers 0.3-0.5(-0.6) mm long, the two anther sacs parallel to divergent. Pistillate flowers pale green, pedicel 0.5-1.5 mm long; sepals lanceolate, narrowly elliptic, or sometimes ovate, 1.4-2.4 by (0.4-)0.6-0.9 mm, sparsely pubescent; ovary 0.8-1.8 by 1-2.7 mm; styles 0.6-1.3 mm long, style 0.4-1 mm long and wide, glabrous or sparsely hairy, stigmas 0.3-0.7 mm long, glabrous, with inner surface stigmatic. Fruits: pedicel 3-4.5 mm long, thick, often distinctly bent; sepals persistent, reflexed; capsules 5-6.5 by 9-11.5 mm, drying dark brown, sparsely covered in stinging hairs. Seeds subglobose, slightly compressed laterally, 4.5-5.5 by 3.8-5.5 by 4-5 mm, smooth or minutely verrucate, coursely mottled dark reddish brown and pale brown.
T h a i l a n d.— NORTHERN: Phayao (Doi Luang National Park); EASTERN: Nakhon Ratchasima; SOUTH-WESTERN: Prachuap Khiri Khan (Hua Hin), Ratchaburi; SOUTH-EASTERN: Chon Buri; PENINSULAR: Satun (Adang).
D i s t r i b u t i o n.— India, Laos, Cambodia, Vietnam, China (Hainan), Java (type), Philippines, Sulawesi, Lesser Sunda Islands.
E c o l o g y.— Scrub, open forest, or forest edge of evergreen, deciduous, or bamboo forest; soil: rocky slopes, rocky granite hill, dry sandy soil. Altitude: 5-600 m
N o t e.— Several collections from Thailand show morphological variation atypical for the species. Kerr 17893 has staminate flowers with two or three anthers rather than the usual two anthers. Kerr 16196 has leaves with 1 or 2 lateral lobes in the apical half.