Perennial or annual herbs; branches terete or quadrangular with simple multicellular hairs. Leaves sessile or petiolate, decussate, simple, entire, crenate, toothed or lobed. Inflorescence leafy, thyrse-like with sessile 1–5-flowered cymes in leaf-axil. Calyx 5-lobed, lobes equal; corolla 2-lipped, but adaxial lip much reduced, lower and lateral lobes of abaxial lip large; stamens 4, fertile, anthers with both locules fertile, strongly divergent; style gynobasic, stigma very shortly bifid. Mericarps not keeled, c. obloid, with a large concavity on the inner surface.
About 40 species, from temperate regions of the Old World; 1 broadly circumscribed species native and 1 naturalised in Australia.