Herbs, rarely somewhat woody, mostly prostrate and branching, with (in our species) opposite or verticillate leaves and solitary cymose or glomerate perfect, small, regular flowers. Stipules none or scarious, or the petiole-bases dilated. Calyx 4-5-cleft or 4-5-parted. Petals small or none in our species. Stamens perigynous, equal in number to the sepals, fewer, or more numerous. Ovary usually free from the calyx, 3-5-celled, and ovules numerous in each cell in our species. Fruit a capsule with loculicidal or circumscissile dehiscence. Seeds am-phitropous; seed-coat crustaceous or membranous; endosperm scanty or copious; embryo slender, curved.

About 22 genera and 500 species, mostly of warm regions, a few in the temperate zones.