Description from Flora of China
Herbs often annual, small, usually glabrous. Roots fibrous. Stems erect or ascending, sometimes ± stoloniferous at base. Leaves opposite, fused at base to form short sheath, flat or terete, margin entire. Inflorescences axillary, cymose, often shorter than subtending leaf, 1- to few flowered. Flowers bisexual, (3 or)4- or 5-merous, inconspicuous. Sepals free, spurless. Petals inconspicuous, free, dull white, greenish, pinkish, or yellowish, often translucent, sometimes shorter than sepals. Stamens as many as petals; filaments filiform. Carpels free. Stigma terminal. Follicles 1- to many seeded, dehiscent along adaxial suture. Seeds smooth, papillate, or striate.
About 16 species: almost worldwide; five species (two endemic) in China.
(Authors: Fu Kunjun (Fu Kun-tsun); Michael G. Gilbert)