Description from Flora of China
Evergreen subshrubs or climbing lianas, epiphytic, less frequently epipetric or terrestrial, not rhizomatous. Stems branched or simple. Leaves usually many, along stem, opposite or whorled, rarely alternate, equal to subequal in a pair; leaf blade glabrous, sometimes puberulent to pilose, base cuneate to subcordate or attenuate. Inflorescences lax, axillary, 1- to many-flowered cymes; bracts 2, opposite. Calyx actinomorphic, 5-sect from base or 5-lobed; segments equal. Corolla purple to reddish, white, or yellow, zygomorphic, inside glabrous, sometimes sparsely puberulent or sparsely glandular puberulent; tube funnelform to tubular, not swollen, longer than limb, 0.3-1.5 cm in diam.; limb 2-lipped; adaxial lip 2-lobed, shorter than abaxial lip; abaxial lip 3-lobed, lobes equal or central lobe longer, apex rounded. Stamens 2, adnate to abaxial side of corolla tube near middle, seldom to near base, included; anthers basifixed, coherent, thecae nearly parallel, not confluent, dehiscing longitudinally; connective sometimes appendiculate; staminodes 2 or 3, adnate to adaxial side of corolla tube. Disc ringlike to cupular. Ovary linear, 1-loculed; placentas 2, parietal, projecting inward, 2-cleft. Stigma 1, terminal, depressed globose, undivided. Capsule straight in relation to pedicel, linear, much surpassing calyx, dehiscing loculicidally to base; valves 2 or 4, straight, not twisted. Seeds with 1 hairlike or subulate appendage at each end.
About 25 species: Bhutan, China, N India, S Japan, Laos, Myanmar, Nepal, N Thailand, N Vietnam; 23 species in China.