Description from Flora of China
Herbs annual or perennial. Stems diffuse or procumbent, much branched. Leaves alternate or opposite, sessile or shortly petiolate; leaf blade oblong, elliptic, or subcordate; stipules small, membranous, caducous. Inflorescence a small cyme or glomerule, sometimes reduced to a solitary flower, leaf-opposed or terminal; bracts small, membranous. Flowers 4- or 5-merous. Pedicel green, short or nearly absent, small. Sepals not aristate at apex, persistent. Petals very small or absent. Stamens as many as and shorter than sepals. Ovary obovoid, 1-locular with 1 to several ovules; style very short, apex 2-fid. Fruit a utricle, a membranous-walled achene enclosed within persistent sepals, irregularly dehiscent or indehiscent, usually 1-seeded. Seeds brown, ovoid or flat-orbicular; testa shiny.
About 45 species: Africa, Europe, and Mediterranean region to C Asia; three species in China.
(Authors: Lu Dequan; Michael G. Gilbert)