Description from Flora of China
Herbs or subshrubs. Leaves entire or dentate. Verticillasters few to many flowered, widely spaced, uniform or reduced in size at end of branches. Calyx tubular to obconical, rarely dilated, 10-veined, straight or curved, truncate or oblique at throat, projected on posterior side; teeth 8-10, usually equal in size. Corolla usually white, rarely yellow, purple, brownish, or scarlet, 2-lipped, tube included; upper lip straight, galeate, densely villous outside; lower lip longer, 3-lobed, middle lobe largest. Stamens ascending beneath upper lip of corolla, close together in pairs; anther cells 2, ovoid, divaricate, apex confluent, often orange. Style unequally 2-cleft at apex, posterior lobe short or obsolete. Nutlets ovoid, triquetrous, subtruncate at apex.
About 100 species: Africa, Asia, Australia, Pacific Islands, two naturalized in South America; eight species in China.