Description from Flora of China
Herbs annual or perennial. Stems diffuse or erect, usually branched. Leaves opposite, sometimes apparently verticillate, sessile or indistinctly petiolate; leaf blade obovate or spatulate; stipules membranous. Inflorescence a cymose cluster, axillary or terminal; bracts scarious. Flowers small. Sepals 5, margin hyaline, midvein raised abaxially into rounded fleshy keel. Petals often fewer than 5, hyaline, less than 1/2 as long as sepals. Stamens 3--5; filaments ± united at base. Ovary 1-loculed with numerous ovules; style short, 3-lobed. Fruit a capsule, 3-valved, several seeded.
About 16 species: tropics and subtropics; one species in China.
(Authors: Lu Dequan; Michael G. Gilbert)