Trigonostemon lii Y.T.Chang

Yu, R. - Y. & Welzen, P. C. van, 2020, A taxonomic revision of Trigonostemon (Euphorbiaceae) outside Malesia, Blumea 65 (1), pp. 25-52 : 37

16. Trigonostemon lii Y.T.Chang — sect. Tylosepalum — Map 8

Trigonostemon lii Y.T. Chang (1983) 175; H. S. Kiu (1996) 166. — Type: Li 4576 (holo KUN, barcode KUN1294357 ), China, Yunnan, Xishuangbanna Botanical Garden .

Shrubs or small trees, 1–4.5 m tall; flowering branches 1.2–2.5 mm diam, pubescent when young, glabrous in old parts. Indumentum of simple hairs; translucent (oil?) dots absent in green parts. Outer bark c. 0.1 mm thick, dark brown to somewhat red- dish brown; inner bark c. 0.1 mm thick, reddish brown to dark red; wood pale yellowish. Stipules subulate, 0.5–0.8 mm long, caducous, often pubescent. Leaves: petiole terete, grooved above, 0.5–2 cm long, 0.9–1.5 mm diam, slightly pubescent when young; blade oblong, 8.5–18 by 2–5.2 cm, coriaceous, base acute, 2 adaxial glands present, margin very distantly serrate, apex acuminate to somewhat caudate, upper surface glabrous, lower surface glabrescent; venation very distinctively triplinerved, midrib slightly raised above and elevated beneath, sometimes slightly pubescent beneath, secondary veins 3–7 pairs, bow-shaped (except for 2 basal secondary veins) and connected along margin, tertiary veins scalariform, veinlets reticulate, obscure. Inflorescences bisexual, terminal or axillary, paniculate thyrses, pistillate flowers single per node, staminate flowers often a cyme per node; main axis terete, 6.5–10 cm long, 0.4–1 mm diam, pubescent; bracts linear to lanceolate, 1–7 by 0.2–1 mm, pubescent. Staminate flowers 6–7 mm diam; pedicel 4–7 mm long, 0.2–0.3 mm diam, slightly pubes- cent; sepals elliptic to lanceolate or oblong, 1.1–2.3 by 0.7–1 mm, base connate, margin entire, apex acute to acuminate, pubescent and often with a notch and a gland outside; petals obovate, 2.8–3.5 by 1.5–2 mm, contort, membranous, yellow, apex rounded, glabrous; disc annular, margin undulate, often deeply notched, c. 0.4 mm wide; stamens 3, androphore c. 0.9 mm long, c. 0.2 mm diam, free part of filaments 0.1–0.2 mm long, white, anthers free, ellipsoid, 0.5–0.6 mm long. Pistillate flowers 7–13 mm diam; pedicel slightly thickening toward apex, 0.8–1.7 cm long, 0.7–1.1 mm diam, slightly pubescent; sepals lanceolate, 2.2–5 by 0.8–2 mm, apex acuminate, pubescent outside; petals flabellate, 5–8 by 5–6 mm, base cuneately nar- rowed, somewhat claw-like, apex rounded; disc cupular, c. 0.3 mm wide, margin undulate, with deep notches; ovary c. 0.9 mm diam, glabrous, style c. 0.2 mm long, stigmas 0.8–1.2 mm long, apex slightly thickened and slightly bifid or not. Fruits c. 1.3 cm diam, green, glabrous; pedicel 1.7–2.65 cm long, 1–1.5 mm diam; sepals persistent but not accrescent; wall 0.6–0.8 mm thick, exocarp not detaching; columella 4.5–7 mm long. Seeds c. 7.5 by 6.5 mm diam; hilum rhombic, c. 1.5 by 1.5 mm.

Distribution — China (Mengla,Menglun, Yunnan), Laos (Luang Prabang).

Habitat & Ecology — Understorey in limestone mountains, often in humid habitats. Elevation: 600– 850 m. Flowering: April to June, September; fruiting: May.

Note — The species can be distinguished from T. eberhardtii by the coriaceous, oblong leaves with very distinctive triplinerved venation and lacking oil dots.

Figures

Map 8 Distribution of Trigonostemon fragilis (Gagnep.) Airy Shaw (●), T. lii Y.T.Chang (★), T. murtonii Craib (▲), T. villosus Hook.f. var. nicobaricus (Chakrab.) N.P. Balakr. & Chakrab. (■) and T. xyphophylloides (Croizat) L.K.Dai & T.L.Wu (X).