Description from Flora of China
Herbs, annual, tending to become anthocyanic with age. Stems erect, glabrous; young branches often 4-angled or narrowly winged. Leaves opposite, usually decussate, sessile or subsessile, membranous. Inflorescences cymose, with small, white, membranous bracteoles. Flowers 4(-6)-merous, actinomorphic. Floral tube campanulate or urceolate, becoming globose or nearly so in fruit, 4(-6)-lobed, noticeably 4-8-veined; sepals short, less than 1/3 length of floral tube; epicalyx segments between sepals small or absent. Petals absent to 4, caducous. Stamens 2-8. Ovary incompletely [1 or]2-4-loculed, globose; ovules numerous; style much shorter to much longer than ovary, style base persistent in fruit; stigma capitate. Capsule globose, hyaline, smooth walled, not finely striated, irregularly dehiscing from apex. Seeds many, golden-brown, obovoid, concave-convex, ca. 1 mm. 2n = 18, 24, 26, 28, 30, 32, 34, 36, 40, 48, 66.
About 25 species: widely distributed in tropical and subtropical areas, mainly in Africa and Asia; four species (one naturalized) in China.
(Authors: Qin Haining (覃海宁); Shirley Graham)