Perennial herb; branches quadrangular; hairs mostly simple. Leaves opposite, petiolate; margin coarsely serrate to crenate, or rarely lobed. Inflorescence of cymose clusters in axils of leaf-like or reduced bracts, often spike-like. Calyx equally 5-lobed, lobes pointed, subequal or abaxial lobes slightly shorter; corolla 2-lipped, abaxial lip with 2 narrow lateral lobes and a broadly spathulate medial lobe, adaxial lip broadly oblong, 2-lobed; stamens 4, fertile, inserted at different levels at and above the throat of the corolla-tube, anthers with 2 fertile, divergent locules, exserted. Mericarps 1-keeled.
About 250 species, from temperate Eurasia, extending to the mountains of tropical Africa; 1 species naturalised in Australia.