Description from Flora of China
Herbs perennial, usually with enlarged rhizomes. Leaves dentate or pinnatifid. Verticillasters sessile, many flowered, subtended by minute bracteoles; floral leaves similar to stem leaves, gradually reduced upward; outer bracteoles equal to longer than calyx. Flowers sessile. Calyx campanulate, ± regular, glabrous inside; teeth 4 or 5, equal or 1 larger. Corolla campanulate, 2-lipped, throat intricately villous; upper lip entire or emarginate; lower lip 3-lobed, middle lobe larger than lateral lobes. Anterior stamens fertile, slightly exserted, straight, posterior 2 rudimentary or filiform, apex clavate or capitate; filaments glabrous; anther cells 2, parallel, becoming divergent. Style exserted, apex 2-cleft; lobes flattened, acute, equal or posterior smaller. Nutlets brown, dorsiventrally flattened, ± adaxially ribbed, glabrous or adaxially glandular, base cuneate, margin thickened, apex truncate.
About 10 species: E Hemisphere, North America; four species in China.