Flora of Thailand
Euphorbiaceae
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Esser & Welzen, Kew Bull. 56: 657. 2001; in Chayam. & Welzen, Fl. Thailand 8, 1: 188. 2005; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11: 169 (sub Croton). 2014.
Subshrubs, hardly and irregularly branched; no latex recorded; monoecious. Indumentum consisting of multicellular, unbranched hairs. Stipules present, very small, eglandular. Leaves alternate; petiole distinct, eglandular; blade simple, symmetric, base attenuate, margin serrate at least apically, glabrous, with a pair of marginal glands near the base, venation triplinerved, tertiary veinlets reticulate, indistinct. Inflorescences terminal, unbranched, elongate, hardly pubescent, bisexual, the basal part with pistillate flowers, the apical one with staminate flowers; bracts very small, eglandular, persistent; flowers one per bract. Flowers actinomorphic, pedicellate. Staminate flowers: sepals 5, the margin ciliate-lanate; petals 5, the margin ciliate-lanate; disc small, lobed, the receptacle distinctly pilose (the flowers therefore filled with whitish hairs); stamens 10-20, erect in bud, filaments longer than the anthers, anthers 2-locular, basifixed; pistillode absent. Pistillate flowers: sepals 5, very large and leaf-like, glabrous; petals and staminodes absent; ovary smooth, glabrous, 3-locular, with 1 ovule per locule; style column distinct, stigmas 3 apically bifid. Fruit pedicellate, 3-locular, dry and dehiscent, glabrous, smooth. Seeds 3 per fruit, ellipsoid, dry, smooth.
Monotypic, endemic to Laos and Thailand. Classification: Subfam. Crotonoideae, tribe Codieae.
1. Colobocarpos nanus (Gagnep.) Esser & Welzen, Kew Bull. 56: 658. 2001; in Chayam. & Welzen, Fl. Thailand 8, 1: 189, plate XII: 1. 2005.— Croton nanus Gagnep., Bull. Soc. Bot. France 72: 464. 1925 & in Lecomte, Fl. Indo-Chine 5: 266. 1925.— Croton colobocarpus Airy Shaw, Kew Bull. 23: 76. 1969; Kew Bull. 26: 245. 1972; Hooker’s Icon. Pl. 38: tab. 3712. 1974.
Subshrub c. 20 cm tall, with a vertical woody rootstock c. 7 cm long. Indumentum pale, c. 0.2 mm long, sparse to absent on vegetative parts. Stipules c. 0.2 mm long, triangular. Leaves: petiole 2-3 mm long, sparsely pubescent; blade obovate, 2-6.5 by 0.5-1.2 cm, length/width ratio 2.5-6.5, thinly chartaceous, base attenuate, margin entire at base, apically serrate, apex acute to obtuse, slightly brighter below; base glands on the basal blade margin, c. 0.4-0.6 mm in diameter, cup-shaped and sessile but prominent, additional glands absent; venation visible on both sides, side veins in 2-3 pairs, triplinerved, arching and indistinctly looped, veinlets indistinct. Inflorescences solitary, c. 2-2.5 cm long, nearly glabrous, with 1 pistillate flower at base, up to c. 10 staminate flowers apically; bracts c. 0.2 mm long, triangular. Staminate flowers: pedicel 2-6 mm long, glabrous; sepals oblong-elliptic, c. 2 by 1 mm; petals oblong-elliptic, c. 2 by 1 mm; stamens 10-20, pilose in lower part. Pistillate flowers glabrous; pedicel 3-5 mm long; sepals c. 5 by 2-3 mm, irregularly ovate-elliptic, with visible pinnate venation, much larger than the ovary; ovary 2 mm long, apically sometimes truncate; style 1-2 mm long, stigmas 1.5-2 mm long, filiform, bifid for c. half the length. Fruits glabrous; schizocarp c. (4-)5-6 by 6-7 mm, slightly trigonal in cross-section and slightly sulcate, apex truncate and surrounded by a corona-like ring to c. 0.8 mm high. Seeds c. 3.5-4 by 3-3.5 cm, flattened-ellipsoid and slightly carinate at side, yellowish-brown, no caruncle seen when dry but with small brownish caruncle when fresh.
T h a i l a n d.— NORTH-EASTERN: Nong Khai (Ban Suwankhiri), Sakon Nakhon (Wanawn - type of C. colobocarpus: Kerr 8479, K, iso A, BK, BM, L).
D i s t r i b u t i o n.— Laos (type), Thailand.
E c o l o g y.— On open grassy ground. Altitude: 200 m.
V e r n a c u l a r.— Plao din (เปล้าดิิน), plao hacho (เปล้าฮาโจ) (General).