Description from Flora of China
Plants annual, biennial or perennial, herbaceous, rarely shrubs. Leaves simple; leaf blade papery, margin dentate to incised, rarely subentire. Verticillasters 2- to many flowered, in false spikes; floral leaves similar to stem leaves or gradually reduced to bracts, rarely dissimilar, larger than stem leaves. Flowers subsessile. Calyx ovoid to globose, campanulate to funnelform, 10-veined, sometimes with inconspicuous accessory veins; teeth 5, slightly irregular. Corolla purple to blue, rarely yellow or white, 2-lipped, often persistent in fruit; tube straight to slightly curved, base slightly bent/swollen; throat slightly dilated, villous annulate, rarely glabrous inside; upper lip straight, entire to 2-lobed; lower lip elongate, 3-lobed, with middle lobe obcordate to nearly flabellate and lateral lobes oblong. Stamens 4, didynamous, exserted from upper lip, involute in bud, anterior 2 longer; filaments straight to slightly curved; anther cells 2, apically confluent. Style subequally 2-cleft, lobes subulate. Nutlets obovoid, triquetrous, netted on back, lateral-ventral side with an areole 1/2-2/3 its length, with an elaiosome.
About 40-50 species: Asia, Europe, especially in the Near East; 18 species in China.