Annual or perennial herbs; stems simple or branched. Leaves alternate, entire to pinnate. Inflorescences cymose, a congested head or solitary and axillary, bracteate. Flowers sessile or pedicellate; sepals 5, herbaceous, becoming chartaceous with age, fused for half the length; corolla 5-lobed, funnel-shaped to trumpet-shaped; stamens equally or unequally inserted in throat of corolla-tube, included or exserted, filaments glabrous; ovary 3-celled, stigma 3-lobed. Capsule 3-celled, 3-valved, chartaceous, dehiscence regular; seeds 1–2 per cell, mucilaginous when wet.
15 species, mostly from to North America, with one species in South America; 3 species recorded in Australia.