Malesian Euphorbiaceae Descriptions
Welzen, P.C. van. 1995. Taxonomy and phylogeny of the Euphorbiaceae tribe Erismantheae G.L.Webster (Erismanthus, Moultonianthus, and Syndyophyllum). Blumea 40: 375396.
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Erismanthus Wall. [Cat. (1846) 8011, nom. nud.] ex Müll.Arg. in DC., Prodr. 15, 2 (1866) 1138; Hook.f., Fl. Brit. India 5 (1887) 405; Ridl., Fl. Malay Penins. 3 (1924) 270; Gagnep. in Lecomte, Fl. Gen. Indo-Chine 5 (1926) 461; Airy Shaw, Kew Bull. 26 (1972) 260; Whitmore, Tree Fl. Malaya 2 (1973) 95; Airy Shaw, Kew Bull. Add. Ser. 4 (1975) 110; Kew Bull. 36 (1981) 294; G.L.Webster, Ann. Missouri Bot. Gard. 81 (1994) 66; Welzen, Blumea 40 (1995) 379; Radcl.-Sm., Gen. Euphorbiacearum (2001) 122; Welzen in Chayam. & Welzen, Fl. Thailand 8, 1 (2005) 261; G.L.Webster in Kubitzki, Fam. Gen. Vasc. Pl. 11 (2014) 107. Type: Erismanthus obliquus Wall. ex Müll.Arg.
Shrubs to trees, monoecious, branching sympodially. Indumentum consisting of simple, short and long (sub)hirsute hairs, glabrescent. Stipules small, interpetiolar, triangular, base broad, margin entire, apex acute, caducous, outside sericeous, inside glabrous. Axillary buds: per node one in axil of a leaf (alternating per node), the other in the axil of a stipule. Petiole reniform in transverse section, not pulvinate, hirsute to sericeous. Leaves simple, distichous, opposite, symmetric; blade punctate; base oblique, cordate; margin slightly serrate (to crenate), with a gland in each tooth; apex rounded to caudate, very apex emarginate to acute; upper surface pustular with white dots, latter forming food bodies in young leaves; lower surface smooth; venation pinnate, looped and closed near the margin, with several pairs of footnerves of which one distinct, above and below slightly raised, tertiary veins obliquely subscalariform, quaternary veins reticulate, inconspicuous. Staminate and pistillate inflorescences separate in same axil, alternating per node; staminate ones short, bract-rich catkins, per bract one flower; pistillate ones with a single flower. Bracts and bracteoles small, triangular to ovate, mainly outside sericeous, bracteoles at base of pedicel of staminate flowers, about halfway pedicel of pistillate flowers. Pedicels subhirsute, to staminate flowers very long. Flowers actinomorphic. Sepals 5, imbricate, basally united, glabrous to subhirsute, in staminate flowers membranous, in pistillate flowers bract- or leaf-like. Petals shorter than sepals, only in staminate flowers, 5, elliptic to obovate, apex rounded or irregular, membranous, glabrous. Disc lobes absent. Stamens in staminate flowers only, 1215, on a short torus, free; filament filiform, glabrous; anther ± triangular, basifixed in deep cleft, opening latrors with a slit, glabrous; connective without an apical triangular appendix. Pistil in pistillate flowers: ovary 3-locular, hirsute; ovules one per locule, descending, epitropous, anatropous, attached in upper half of column; style 1, short, hirsute; stigmas 3, apically split into two lobes, above with papillae, below hirsute; in staminate flowers only a long style with a bifid or trifid apex left. Fruit a 3-lobed rhegma, subglobose, outside sericeous, glabrescent, inside glabrous, dehiscing septi- and loculicidally into 6 segments; wall thin, woody, on inside with light short stripes in E. sinensis; septum with one splitting vein; column after dehiscense with a narrow, straight septum margin attached to it, apically broadened. Seeds 13 per fruit, brown, glossy, micropyle well visible, with light brown short longitudinal stripes; arilloid absent. Embryo not seen.
Distribution Two species, one present in SE Asia (S China, Laos, Cambodia, Vietnam, northern half of Thailand) and the other in Malesia: Peninsular S Thailand and Malaysia, Sumatra, and Borneo.
Note The axillary buds are very typical, per node one bud is still found in the axil of a leaf, but the other one is in the axil of one of the stipules.
Erismanthus obliquus Wall. [Cat. (1846) 8011, nom. nud.] ex Müll.Arg. in DC., Prodr. 15, 2 (1866) 1138; Hook.f., Fl. Brit. India 5 (1887) 405; Pax & K.Hoffm. in Engl., Pflanzenr. IV.147.iii (1911) 34; Merr., J. Str. Br. Roy. Asiat. Soc., spec. numb. (1921) 346; Ridl., Fl. Malay Penins. 3 (1924) 271; Gagnep. in Lecomte, Fl. Gen. Indo-Chine 5 (1926) 464 ('obliqua'); Airy Shaw, Kew Bull. 26 (1972) 260; Whitmore, Tree Fl. Malaya 2 (1973) 95; Airy Shaw, Kew Bull. Add. Ser. 4 (1975) 110; Kew Bull. 36 (1981) 294; Welzen, Blumea 40 (1995) 381, Fig. 2, Map 1; in Chayam. & Welzen, Fl. Thailand 8, 1 (2005) 261, fig. 66, plate XVI: 1. Type: Wallich 8011 (K, holo; iso in L), Malaysia, Penang.
Tree up to 17 m high, d.b.h. up to 20 cm; girth up to 67 cm; bole fluted; flowering branches 1.25 mm thick, smooth, (sub)hirsute when young. Outer bark sandy brown to grey, smooth, thin; inner bark pale brown mottled. Sapwood white. Leaves: stipules 4.313 by 1.23.3 mm; petiole 14 mm long, often reddish when dry; blade elliptic, 723 by 2.58.2 cm (mostly more than 10 cm long), index 2.32.8, chartaceous, margin flat, apex acuminate to caudate, very apex rounded to acute, above and below (sub)glabrous, nerves 811 per side. Staminate catkins 79 by 3.54 mm when without flowers, brown; peduncle 12 mm long. Bracts to the catkins c. 4.5 by 1 mm; bracts to the flowers c. 1.63 by 0.30.4 mm, long acute. Staminate flowers c. 2 mm in diam., green to pale yellow brown to cream; pedicel more than 1.5 cm long; sepals elliptic to obovate, 0.91.5 by 0.50.7 mm; petals 11.2 by c. 0.5 mm; stamens 15, filament 0.30.6 mm long, anther 0.60.9 by 0.41 mm; stigma remnant up to 4.8 mm long. Pistillate flowers c. 2 cm in diam., green to orangy pink; pedicel 2.86.5 mm long; sepals leaf-like, ovate, 5.517 by 3.36 mm, margin slightly serrate, with glands, apex acute, outside and margin subsericeous, inside glabrous; ovarium ovoid, 1.22 by 1.82.5 mm, style 1.23.3 mm long, stigmas 1.32.4 cm long, upper 11.6 cm bifid. Fruits 1314 mm broad by 89 mm high, pale yellow; wall 0.50.7 mm thick. Seed ± globose, 46 mm in diam.; hilum c. 0.8 mm long. Embryo not seen.
Distribution Malesia: S Peninsular Thailand, Peninsular Malaysia, N Sumatra (2 specimens), NE and S Kalimantan (2 specimens). See map 1; the dot in Sumatra only indicates the possible collection site.
(dots; squares is E. sinensis Oliv. in S.E. Asia mainland, outside Malesia).
Habitat & Ecology Found in (slightly disturbed) rain forest, often along rivers. Common in undergrowth. Soil: limestone. Alt.: 30360 m. Male catkins whole year through. Flowering: February to October; fruiting: February to August.
Vernacular name Peninsular Malaysia: Bekoi (Asli).