Herbs annual or perennial, rarely biennial. Stems erect or rarely creeping, often caespitose or pulvinate. Leaves opposite, rarely whorled; leaf blade linear to elliptic, ovate, or orbicular, usually flat, margin entire. Flowers solitary or numerous in cymes, actinomorphic. Sepals 4 or 5, apex entire, rarely emarginate. Petals 4 or 5, sometimes absent, apex entire to toothed, 2-cleft, or fimbriate. Stamens (2--5 or 8 or)10. Ovary 1-loculed; ovules numerous. Styles 2 or 3(--5). Capsule ovoid, obovoid, or globose, usually shorter than persistent sepals, rarely equaling or longer than them, 3- or 6-valved. Seeds reniform or subovoid, flattened, smooth, tuberculate, or narrowly winged.

Arenaria has been subdivided into ten subgenera, several of which were further divided into sections and series (McNeill, Notes Roy. Bot. Gard. Edinburgh 24: 79–155. 1962). Six subgenera are represented in China, one of which ( A. subgen. Odontostemma ) contains more than half the species.

Arenaria ladyginii Kozhevnikov (Novosti Sist. Vyssh. Rast. 21: 67. 1984) was described from Xizang. However, the type has not been seen by the present authors and its identity could not be ascertained.

More than 300 species: N temperate to arctic regions; 102 species (79 endemic) in China.

(Authors: Wu Zhengyi; Warren L. Wagner)