Description from Flora of China
Trees, deciduous, evergreen in tropics. Bark smooth with conspicuous lenticels when young, longitudinally splitting with age. Branches opposite, without terminal buds. Leaves opposite, occasionally 3 in a whorl; petiole long; leaf blade entire or shallowly 3-5-lobed, margin undulate and often serrate when young. Inflorescences a large pyramidal to cylindric thyrse. Cymes (1-)3-5(-8)-flowered, pedunculate or not. Calyx campanulate or obconical, hairy; lobes 5, subequal, upper 1 enlarged. Corolla purple or white, funnelform-campanulate to tubular-funnelform; tube base constricted and slightly curved; limb 2-lipped; lower lip elongated and 3-lobed; upper lip yellow, 2-lobed. Stamens 4, didynamous; filaments included, twisted near base; anthers divergent. Ovary 2-loculed. Style nearly as long as stamens. Capsule loculicidal, 2-valved or incompletely 4-valved; pericarp thin or thick and woody. Seeds small, numerous, membranous winged; endosperm sparse.
Seven species: mostly in China with one species extending to Laos and Vietnam; six species in China.
Because of the extensive cultivation of most species, it is often difficult to determine the precise wild distribution.