Description from Flora of China
Herbs annual. Stems erect or ascending, divaricate branched. Leaves petiolate; leaf blade ovate-lanceolate or lanceolate, margin dentate. Verticillasters 6- to many flowered, remote or crowded upward; bracts minute, linear or lanceolate. Flowers sessile. Calyx tubular-campanulate, 5-10-veined; teeth 5, equal or posterior ones longer, rigidly subulate-spinescent. Corolla white, yellowish, or purple, spotted, 2-lipped; tube straight, exserted, funnelform, without hairy annulus inside, throat enlarged; upper lip erect, concave, ovate, margin entire or dentate, hairy outside; lower lip spreading, 3-lobed; middle lobe obcordate, emarginate, or subrounded, dentate at junction with lateral lobes; lateral lobes ovate. Stamens 4, parallel, ascending beneath upper lip; anther cells 2, dorsifixed, dehiscing transversely by 2 valves, inner valves smaller, ciliate, outer valves larger, glabrous. Style apex 2-cleft, lobes subulate, subequal. Disc truncate at apex or anterior lobe swollen. Nutlets broadly obovoid, nearly flattened abaxially, smooth, obtuse at apex.
About ten species: mainly in Europe, Asia; one species in China.