Perennial herbs; stems trailing or ascending, often rooting at nodes, densely covered with appressed medifixed hairs. Leaves undivided, usually serrate-dentate, often fleshy. Inflorescence spicate, axillary, pedunculate, usually at first capitate, later cylindric, densely many-flowered. Flowers sessile, each in the axil of a single bract; calyx membranous, ovoid-campanulate or compressed; corolla cylindric, 2-lipped and 4-partite, lobes spreading, rounded or emarginate; stamens in 2 unequal pairs, included near the middle of the corolla-tube or scarcely exserted; ovary 2-locular, 1 ovule per locule. Fruit small, dry, enclosed by the calyx, ellipsoid, compressed, breaking into 2 mericarps.
10 species in tropical and subtropical America, and 1 or 2 species in warmer parts of Eurasia; 1 species naturalised in Australia.