Annual or perennial, usually small herbs, glabrous or glandular hairy, richly branched, forming loose tufts or mats, or dense cushions. Leaves exstipulate, very narrow, opposite, slightly connate at the base, with or without ciliate margin. Flowers axillary, solitary or in few-flowered cymes; Sepals 4 or 5, erect or patent. Petals white, 4 or 5, entire, ovate or obovate, sometimes minute or absent. Stamens 4-5 or 8-10, the inner episepalous with a nectarial gland at the base. Ovary ovoid; Capsule ovoid to cylindrical, opening ± to the base by 4 or 5 valves. Seeds numerous, very small (0.2-0.5 mm), dark brown, reniform, papules.
Africa present, Asia-Temperate, Asia-Tropical: New Guinea present, Ethiopia present, Himalayan region present, Japan present, North and South America present, Pacific: Hawaii present, the Mediterranean present
About 25 species, widely distributed particularly in the temperate zone of the northern hemisphere. In America especially along the Cordillera in both North and South America. In Africa besides the Mediterranean region occurring in Ethiopia. Several species in the Himalayan region, through China to Japan, New Guinea, New Zealand and Hawaii. In Malesia 7 species.
About 25 species; the specific delimitation, however, is in many cases uncertain. There is no recent monograph and the genus is in need of a thorough revision. The arctic-alpine species were dealt with by
An unpublished study by J.F. Veldkamp (L), Dutch, and Indonesian students from Herbarium Bogoriense (BO) and University Padjadjaran, Bandung (FMIPA) has been a great help in the revision of this genus.