Herbs creeping, glabrous or slightly tomentose. Leaves opposite, margin entire. Flowers perfect, densely clustered in heads. Heads terminal or axillary, globose or terete. Bracts papery; bracteoles keeled, without distal crest. Tepals 5, with short claw at base. Stamens 5; filaments subulate, connate into a cup at base, lateral appendages absent, pseudostaminodes absent; anthers 1-loculed. Ovary ovoid, compressed; style very short; stigma 2-parted; ovule 1, pendulous. Seeds shiny, lenticular.

About 15 species: W Africa, E Asia, E North and South America, Pacific Islands; one species in China.