Malesian Euphorbiaceae Descriptions
Forster, P.I. & P.C. van Welzen. 1999. The Malesian species of Choriceras, Fontainea, and Petalostigma (Euphorbiaceae). Blumea 44: 99–107.
van Welzen, P.C. & Forster, P.I. 2011. Picrodendraceae (formerly Euphorbiaceae s.l. subfam. Oldfieldioideae). In: Nooteboom, H.N. (ed.), Flora Malesiana ser. 1, 20: 45–61.
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Choriceras Baill., Adansonia 11 (1873) 119; Airy Shaw, Kew Bull. 14 (1961) 356; Kew Bull. 16 (1963) 344; Kew Bull. 35 (1980) 604; Kew Bull. Add. Ser. 8 (1980) 46; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 58; P.I.Forst. & Welzen, Blumea 44 (1999) 100; Radcl.-Sm., Gen. Euphorbiacearum (2001) 94; Welzen & P.I.Forst. in Noot., Fl. Males. ser. 1, 20 (2011) 55; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 101. — Type: Choriceras australiana Baill. [= Choriceras tricorne (Benth.) Airy Shaw]
Shrubs or trees, evergreen, perennial, monoecious; branchlets puberulous; stems and foliage without latex. Indumentum of simple, multicellular hairs, glandular and stinging hairs absent. Stipules entire, inconspicuous, caducous. Leaves opposite, petiolate, ovate to elliptic, coriaceous, penninerved, (sub)entire or crenate to serrate, glands absent. Inflorescences axillary, with bracteate solitary or fascicles of flowers. Flowers unisexual, actinomorphic, pedicellate, sepals in 2 whorls, imbricate, free, ± equal, petals and disc absent. Staminate flowers in dense multiflowered fascicles; sepals 2+2 or 3+3; stamens 4 or 6, filaments free, inserted on slightly raised receptacle, anthers dorsifixed, bilobate, thecae globose and longitudinally dehiscent. Pistillate flowers 1–3 together; sepals 3+3; ovary 3- or 4-locular, 2 ovules per locule; style short; stigmas simple, not split. Fruits capsular, trilobate, smooth, dehiscing septicidally into 3 bivalved cocci; lobes horned with stigma remnants. Seeds ovoid; testa crustaceous; albumen fleshy; caruncle absent; cotyledons broad, flat.
Distribution — Two species in Australia, one extending to New Guinea.
Choriceras tricorne (Benth.) Airy Shaw, Kew Bull. 14 (1961) 356; Kew Bull. 35 (1980a) 604; Kew Bull. Add. Ser. 8 (1980b) 46; P.I.Forst. & Welzen, Blumea (1999) 100, Fig. 1; Welzen & P.I.Forst. in Noot., Fl. Males. ser. 1, 20 (2011) 55, fig. 3. — Dissiliaria tricornis Benth., Fl. Austral. 6 (1873) 91; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.xv (1922) 292. — Lectotype (designated by Airy Shaw, 1980a): A. Cunningham 265 (K), Australia, Northern Territory, Port Essington.
Choriceras australiana Baill., Adansonia 11 (1873) 119. — Type: Leguillou s.n. (P), Australia, Northern Territory, Raffles Bay.
Shrubs to small trees up to 7 m high, often multistemmed. Outer bark grey to brown, rough to flaky; inner bark streaky dark pink to red; cambium furrowed; sapwood pale amber, rather hard; heartwood dark pink. Indumentum of uncoloured to yellow-ferruginous simple hairs, glabrescent unless stated otherwise. Stipules subulate, 1–1.8 by c. 0.3 mm, densely pubescent. Leaves: petioles 2–7 by 0.8–1 mm, (sub)glabrous to densely pubescent; lamina elliptic to elliptic-lanceolate, 10–90 by 4.5–32 mm, index 2.2–2.8, base cuneate to truncate; margins crenate to serrate with 20–40 short teeth; apex obtuse to acute; strongly discolorous, upper surface dark glossy green, glabrous or with scattered hairs on the midrib; lower surface pale green, subglabrous; venation comprising 6–8 nerves per side, veins reticulate, indistinct. Inflorescences up to 10 mm long. Staminate flowers 2.3–4 by 2–3 mm diam., cream-yellow; pedicels 2.6–9 by c. 0.1 mm diam., glabrous; sepals orbicular to lanceolate, 1–1.6 by 0.7–0.9 mm, glabrous; stamens 4 or 6; filaments 1.2–2 by c. 0.1 mm, basally sparsely to densely hairy; anthers globose, 0.4–0.6 by 0.3–0.5 mm. Pistillate flowers 2–3.5 by 2.4–4.5 mm diam.; pedicels 1.5–2 by c. 0.4 mm diam., with scattered hairs; sepals lanceolate-ovate, 1.5–1.8 by 1–1.3 mm, glabrous or with scattered hairs; ovary usually 3-locular, subglobose, 1–1.5 by 2–2.5 mm diam., glabrous; styles 1.5–2.5 mm long, strongly recurved, papillose. Fruits globose, 4–7 by 5–11 mm diam., green-grey. Seeds ovoid, 3.5–4.8 by 2.5–3 by 2–3 mm thick, smooth, pale brown.
Distribution — N Australia (Northern Territory and Queensland) and in Malesia: New Guinea (SE Irian Jaya and Western Province in Papua New Guinea).
Habitat & Ecology — Heathland, savannah with Acacia, Eucalyptus, and Melaleuca, open forest, vine thickets, and margin of rain forest, usually on sandy soils, also on reddish loam. Alt.: sea level up to 400 m. Flowering and fruiting throughout the year after heavy rain.