Description from Flora of China
Ancylostemon saxatilis (Hemsley) Craib var. microcalyx (Hemsley) Craib; Didissandra saxatilis Hemsley var. microcalyx Hemsley.
Petiole to 5.5 cm, rust-brown villous; leaf blade elliptic to lanceolate, 1.1-4.4 X 0.7-1.8 cm, adaxially sparsely brown villous, glabrescent, abaxially pubescent, densely rust-brown villous abaxially along veins, base cuneate to subcordate, margin crenate to serrate; lateral veins 3-5 on each side of midrib, adaxially indistinct, abaxially conspicuous. Peduncle 3-8 cm, brown villous and sometimes glandular pubescent; bracts linear to oblong or elliptic, 2-4 X ca. 1 mm, glabrous to sparsely villous. Calyx 5-sect from base; segments oblong to triangular, 1.5-2 mm, outside sparsely pubescent, glabrescent, margin entire. Corolla yellow-white, 1.1-1.5 cm; limb 2-lipped; adaxial lip ca. 2 mm, 2-lobed, lobes thickened at apex; central lobe of abaxial lip subovate, ca. 3.5 mm, lateral ones narrowly ovate, ca. 1.8 mm. Adaxial stamens included, ca. 9 mm, abaxial ones exserted, 5-8 mm; filaments glabrous; staminode ca. 3.5 mm. Disc ca. 1.3 mm, subentire. Pistil 8-10.5 mm, glabrous. Capsule 2-4 cm. Fl. Jul.
* Stones in forests and damp limestone hills; ca. 2100 m. W Hubei, SE Sichuan.