Annual, rarely perennial, mat-forming herbs, glabrous or hairy. Leaves opposite, or the upper pseudo-alternate by abortion; stipules silvery-scarious; bracts small, scarious. Flowers in dense axillary clusters, 4(–5)-merous, unisexual or bisexual; sepals 5, free; petals minute, subulate, often absent; stamens 2–5; ovary 1-celled with 1 basal ovule, style 1, bifid above. Fruit an indehiscent achene enclosed by persistent calyx; seed 1, lenticular, smooth and glossy.
About 35 species in Europe and the Mediterranean region, south-western Asia and South Africa; 1 species naturalised in Australia.