Description from Flora of China
Herbs annual or perennial, or subshrubs, often with thick roots. Stems erect, glabrous; axils naked. Leaves alternate or partly opposite, sessile or shortly petiolate, flat. Inflorescence terminal or rarely axillary, a thyrse or panicle, very rarely flowers solitary. Sepals free or shortly connate at base, caducous. Petals 5(-10), free. Stamens 5-30, usually adnate to base of petals. Ovary superior. Stigma (2- or)3-lobed. Capsule 3-valved, often recurved, globose, ovoid, or ellipsoid. Seeds glossy black-brown or black, subglobose or oblate, orbicular-reniform, tuberculate or ribbed, with pale caruncle.
About 50 species: mainly in warm regions of the Americas, a few species native to Africa and Arabia, mostly introduced in Asia; one species (introduced) in China.