Description from Flora of China
Herbs annual or perennial, glabrous. Stems diffuse, decumbent, or erect, branched or not, sometimes absent. Leaves in a basal rosette, pseudoverticillate, opposite, or whorled, ± sessile, margin entire. Inflorescences terminal or seemingly leaf-opposed cymes or umbels. Flowers pedicellate. Tepals 5, rarely 4, free, herbaceous, often with transparent scarious margins. Stamens usually 3(-5), rarely more (6-10). Carpels 3(-5), connate; ovary superior, ovoid or ellipsoid, 3(-5)-loculed, each locule with many ovules on axile placenta. Styles 3(-5), linear. Capsule globose, membranous, 3(-5)-valved, loculicidal, with persistent tepals. Seeds numerous, reniform or D-shaped, smooth, sculptured, or raphe ribbed, without filiform arils or caruncles; embryo annular.
About 35 species: mostly in tropical and subtropical regions, extending into warm-temperate regions of Europe, E Asia, and North America; four species in China.