Plants annual or perennial, prostrate, erect, or strangling or twining herbs, or cushionlike or erect shrubs; axial parts usually pubescent, hairs simple or 2-armed. Leaves simple, petiolate or sessile, margin entire or ± lobed. Flowers axillary, peduncled, solitary or in various kinds of inflorescences. Sepals equal or unequal, middle sepal asymmetric (exposed 1/2 similar to outer 2 sepals, enclosed 1/2 similar to inner 2 sepals), persistent, not enlarged. Corolla funnelform or campanulate; limb shallowly lobed or entire, with 5 ± distinct midpetaline bands. Stamens included, inserted at corolla base; filaments dilated basally, filiform apically; pollen ellipsoid, 3- (or 4)-colpate, not spiny. Disc ringlike or cupular. Pistil included; ovary 2-loculed; ovules 2 per locule. Style 1, filiform; stigmas 2, linear, cylindric, or clavate. Capsule 2-loculed, 4-valved or irregularly dehiscent. Seeds 1-4, black or brown, often verruculose, pubescent, rarely glabrous.

Approximately 250 species: widely distributed; eight species in China.