Description from Flora of China
Herbs erect perennials or diffuse annuals, rarely subshrubs or shrubs, sometimes rhizomatous. Verticillasters 2- to many flowered, in terminal spikes. Pedicel short or obsolete. Calyx tubular-campanulate, obconical or tubular, 5- or 10-veined; teeth 5, equal or posterior 3 larger, acute to bristlelike, or spinescent. Corolla red, purple, yellow, gray, or white, 2-lipped; tube cylindric, nearly always villous annulate inside, sometimes saccate, incurved at apex, throat not dilated; upper lip straight or subpatent; lower lip longer, 3-lobed, middle lobe entire or emarginate, lateral lobes shorter. Stamens 4, reaching upper lip of corolla, anterior 2 longer and curved laterally at corolla throat; anther cells 2, conspicuous, parallel or divergent. Style apex subequally 2-cleft, lobes subulate. Nutlets ovoid to oblong, smooth or tuberculate, apex obtuse to rounded.
About 300 species: Africa, Asia, Europe, North America, South America; 18 species in China.