Trigonostemon thyrsoideus Stapf, Bull. Misc. Inform. Kew 1909: 264 (1909)

Diagnostics
Shrubs or small trees up to 6 m high. Leaves evenly spaced; petiole 1-11 cm; Leaf blade glabrous, obovate, margins sparsely serrate, venation pinnate, apex shortly acuminate to acuminate; Inflorescences branched; flowers yellow, stamens 5.

Description
Shrubs or small trees up to 6 m high; branchlets sparsely hairy, glabrescent. Stipules triangular, c. 1 mm long. Leaves: petiole very variable in length, (2.5-)7.5-14 cm long, sparsely hairy; blade elliptic to obovate to oblong, (10.5-)13-24 by 3.5-9.5 cm, membranous or thinly chartaceous, glabrous on both sides, base cuneate or subobtuse, margin broadly, distantly and shallowly crenate, apex acute to caudate; venation triplinerved, sparsely hairy, glabrescent, nerves in 9-15 pairs. Inflorescences pyramidal thyrsoid, terminal, up to 20 cm long, adpressed puberulous, branches angled or flattened. Staminate flowers: pedicel 2-5 mm long; sepals ovate-elliptic, c. 1.5 by 1 mm, pubescent outside, margin membranous; petals oblong, 3-3.5 by 1.8-2 mm, glabrous, yellow; disc glands 5, obovate-oblong; stamens 5, c. 1.5 mm long, staminal column minute, c. 1 mm long, anthers c. 0.25 mm long, with appendage up to 0.25 mm long. Pistillate flowers: pedicel 3.5-4 mm long; sepals ovate-elliptic, c. 1.5 by 0.8-1 mm long, pubescent outside, margin membranous; petals oblong, c. 4 mm by 1-1.5 mm, glabrous, yellow; disc glands 5; ovary glabrous; style c. 0.1 mm long. Fruits: pedicel 2.7-4.2 cm; capsule 1.2-1.5 cm in diameter, sparsely and shortly aculeate. Seeds slightly globose, 6-7 mm in diameter. [from Flora Malesiana]

Ecology
In evergreen or pine-dipterocarp forest. Altitude: 600-1500 m.

Distribution
Myanmar, Southern China, Northern Thailand, Laos, Vietnam.

Local names
China: Chang geng san bao mu.