Shrubs or annual or perennial herbs; pubescence of simple sometimes glandular hairs. Leaves petiolate; leaf blade simple, entire or sinuate-dentate. Inflorescences solitary flowers in leaf axils or in branch forks; peduncle, bracts, and bracteoles absent. Flowers actinomorphic, large. Pedicel often stout. Calyx long tubular or cylindric, often circumscissile near base. Corolla elongated, funnelform; lobes sometimes cuspidate. Anthers mostly elongated, dehiscing longitudinally, included. Ovary 2-4-locular. Fruit a dry capsule, 4-valved or irregularly dehiscent, prickly or unarmed, often subtended by remnants of persistent calyx. Seeds numerous, laterally compressed; embryo curved.

About 11 species: North and South America, three species in China.