Description from Flora of China
Herbs or shrubs, with cystoliths. Leaf blade margin entire or slightly toothed. Inflorescences in axillary or terminal cymes, these sometimes aggregated into a leafy panicle-like complex; cymes consisting of (1 or)2-4(or more) involucres; involucres of usually 1-3 flowers enclosed by 2(or more) pairs of bracteoles that conceal calyx and corolla tube. Outer pair of bracteoles equal to unequal in size and larger than inner pair(s). Calyx small, 5-lobed; lobes equal. Corolla white to pink or purple, usually large, resupinate 180°; tube slender, twisted, apically ± widened into throat; limb 2-lipped; upper lip (in lower position) entire to 2-cleft; lower lip (in upper position) 3-lobed; lobes ascending cochlear in bud. Stamens 2, inserted at corolla throat, exserted from corolla tube; anthers 2-thecous; thecae unequally inserted or superposed (contiguous or separated by gap), base muticous; staminodes absent. Ovary with 2 ovules per locule; stigma slightly enlarged or 2-cleft. Capsule with a solid stalk, 4-seeded; retinacula present; placenta not rising elastically from base of valves. Seeds discoid, smooth to tuberculate, lacking trichomes.
About 40 species: tropical and subtropical Africa, Asia, and Madagascar, with one species possibly extending to Australia (see R. M. Barker, J. Adelaide Bot. Gard. 9: 192. 1986); ten species (three endemic) in China.
(Authors: Hu Jiaqi (胡嘉琪 Hu Chia-chi), Deng Yunfei (邓云飞); Thomas F. Daniel)