Brachiostemon macrocalyx Handel-Mazzetti.

Stems 20-40 cm, villous to pubescent. Petiole 2-11 cm; leaf blade ovate to broadly ovate, seldom obovate, 5-13 X 2.5-10 cm, sparsely pubescent, abaxially villous along veins, margin dentate-serrate, sometimes double, apex acuminate to acute. Peduncle 1.7-3.6 cm, villous; bracts 4-7 mm. Pedicel 0.9-2 cm. Calyx segments spreading, lanceolate to narrowly obovate, 0.7-1.4 cm X 2-3 mm, outside pubescent to villous. Corolla white, flushed purplish, 1.2-1.5 cm; tube 6-9 X 6-8 mm; adaxial lip ca. 6 mm, glabrous inside, lobes ca. 2 mm; abaxial lip 3-7 mm, yellowish bearded, lobes oblong, 2-3.5 mm. Stamens ca. 3 mm; filaments forked apically, glandular puberulent near apex; 1 branch with fertile anther, other with a thick yellow knob; staminodes 2, 1-2.5 mm. Ovary ovoid to broadly ovoid, 2-3 mm, villous. Style 4-9 mm, puberulent. Capsule 1.5-1.8 cm. Fl. and fr. Jul-Sep.

Rocks at forest margins; 300-1300 m. SW Guangxi, S Yunnan [NW Thailand].