Malesian Euphorbiaceae Descriptions
Welzen, P.C. van & P.I. Forster. 2012. Five rare genera of Euphorbiaceae (sensu lato) in the Malay Archipelago: Alphandia, Ashtonia, Borneodendron, Cladogynos and Tapoοdes. Edeninburgh J. Bot. 69: 389411.
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Borneodendron Airy Shaw, Kew Bull. 16 (1963) 358; Kew Bull. 25 (1971) 504, in obs.; Kew Bull., Addit. Ser. 4 (1975) 60; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 110; Govaerts, Frodin & Radcl.-Sm., World Checkl. Bibliogr. Euphorb. 1 (2000) 274; Radcl.-Sm., Gen. Euphorbiacearum (2001) 315; Welzen, Edinburgh J. Bot. 69 (2012) 398; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 178. Type: Borneodendron aenigmaticum Airy Shaw.
Trees, probably monoecious, branching verticillate in twos and threes. Indumentum of dark ferruginous stellate and simple hairs. Stipules united, circumaxillary, covering terminal bud, shed when bud develops. Leaves verticillate in groups of three, alternate, at end of branchlets, simple, covered with stellate hairs when very young; petiole flattened and slightly grooved above, not pulvinate, often with two or more glands halfway to apically; blade thick coriaceous, symmetric, venation pinnate, very dense with the many nerves and intercalary nerves perpendicular to the midrib. Inflorescences terminal, staminate one racemose, short, with c. 3 nodes, each with 3 flowers subtended by large bracts, peduncle nodding, dense stellate hairs; bracts outside with stellate hairs, inside mainly with simple hairs; pistillate flowers three together on the upper nodes, each flower single in axil of leaf. Flowers yellow; pedicels flattened; calyx 3-lobed, splitting regularly, valvate, caducous, outside with mainly simple hairs, inside glabrous; petals and disc absent. Staminate flowers on short pedicels, stamens 2530, inserted on a columnar receptacle, filaments very short, strap-like, anthers basi-dorsifixed, 2-thecate, thecae above splitting apart, opening latro-extrorse via lengthwise slits, connective indistinct; pistillode absent. Pistillate flowers on short pedicels; ovary 2-locular, ovules 1 per locule, style absent, stigmas split, first split to c. 4/5, each lobe split again for 1/32/3, above with a few, indistinct tubercles. Fruits capsules, splitting completely septicidally and partly (apically) loculicidally into two 2-valved cocci; pedicel elongated, long, thickened towards apex; calyx remnants recurved; wall thick, woody; columella very narrow, basally and apically somewhat thickened. Seeds often marbled, smooth, with very small caruncle.
Distribution A single species endemic to N Borneo (Sabah).
Borneodendron aenigmaticum Airy Shaw, Kew Bull. 16 (1963) 359; Hookers Icon. Pl. 37 (1967) Tab. 3633; W.Meijer, Bot. News Bull. Forest Dep. Sabah 7 (1967) 24; Bot. Bull. Herb. Forest Dep. Sabah 10 (1968) 10, 229; Airy Shaw, Kew Bull., Addit. Ser. 4 (1975) 60; Govaerts, Frodin & Radcl.-Sm., World Checkl. Bibliogr. Euphorb. 1 (2000) 275, fig. p. 276; Welzen, Edinburgh J. Bot. 69 (2012) 399, Fig. 4. SAN (M. Chai) 21695 (holo K; iso L), Malaysia, Sabah, Pulau Sakar.
Trees, probably monoecious, up to 40 m high, bole up to 25 m high, d.b.h. 19 cm; buttressed (Radcliffe-Smith 2001); flowering branches up to 5 mm thick, somewhat fleshy, slightly shrivelled when dry, with many leaf scars. Outer bark smooth to flaky, grey; inner bark pink to reddish brown to pale brown, exudate reddish, fast to appear; sapwood dark brown. Stipules united, up to 16 mm high, at least outside densely covered with stellate hairs. Leaves: petiole 1.83 cm long; blade elliptic to oblong to obovate, 4.222 by 1.77.9 cm, length/width ratio 1.92.8, base attenuate, margin entire, recurved, apex slightly emarginate to very shortly acuminate, upper and lower surface glabrous when mature, smooth, venation slightly raised on both sides, slightly less above, nerves 1430 per side, looped and close near margin, hardly distinguishable from the intercalary nerves, veins and veinlets reticulate. Staminate inflorescences: peduncle c. 15 mm long, flattened, stellately hairy; bracts long ovate, c. 11 by 2.8 mm, outside stellately hairy, inside mainly simple hairs. Staminate flowers c. 6 mm in diam. (young); pedicel c. 3 mm long, hairy, indumentum of mainly simple hairs; calyx lobes ovate, c. 3.3 by 3.5 mm; stamens: filaments c. 0.45 mm high, glabrous, anthers oblong, c. 1.3 by 1 mm, with a few simple hairs. Pistillate flowers c. 3 mm in diameter (excluding stigmas); pedicel c. 4 mm long, elongating in fruit, hairy, indumentum of mainly simple hairs; calyx lobes (young) ovate, c. 2.8 by 2 mm; ovary ovate, c. 2 by 2 mm, covered with stellate hairs, stigmas 3.53.8 mm long. Fruits flattened ellipsoid, 2.32.9 cm high by c. 2 cm broad, (sub)glabrous, greenish when immature; pedicel elongated up to 5.8 cm; wall 23 mm thick; columella 1.752 cm long. Seeds ellipsoid, flattened inside, 1415 by 8.59.5 by 7.58 mm.
Distribution Borneo: Sabah.
Habitat & Ecology Primary forest, on hills, along roadside; soil: ultrabasic rock. Altitude: 50600 m. Flowering: April, May; fruiting: May, June, August.
Vernacular name Bangkau bangkau.
Note The specific epithet indicates that the genus/species is enigmatic with regards to its classification. It was classified by Webster (1994) and Radcliffe-Smith (2001) in subfam. Crotonoideae tribe Ricinocarpeae subtribe Bertyinae Mόll.Arg. together with Bertya Planch., Myricanthe Airy Shaw, and Cocconerion Baill., following what Airy Shaw suggested in 1971. Radcliffe-Smith (2001) also discusses simularities with taxa in subtribe Mischodontinae of the former subfamily Oldfieldioideae (now the Picrodendraceae), taxa with 2 ovules per locule.