Herbs, rarely low shrubs, perennial, semi-aquatic, usually erect, glabrous or glandular pubescent, sometimes with axillary spines. Leaves alternate, simple, entire or serrulate. Inflorescences terminal or axillary, commonly corymbose or paniculate. Calyx persistent; lobes nearly distinct. Corolla blue or white, rarely purple, campanulate to rotate. Stamens 5, inserted at base of corolla tube; filaments dilated at base; anthers 4-lobed, basifixed. Ovary usually 2-locular; ovules numerous; placentation axile. Styles 2. Capsule ovoid, globose, or ellipsoid, dehiscing longitudinally or irregularly; pericarp thin. Seeds numerous, seed coat longitudinally ridged and reticulate.

Eleven to 20 species: Africa, Asia, Australia, North America, South America; one species in China.