Description from Flora of China
Herbs or shrubs. Leaves crenate to serrate. Verticillasters in axils or upper leaves, 2-10-flowered. Calyx campanulate, membranous, dilated after anthesis, 10-veined, 4- or 5-toothed; teeth triangular, equal or subequal, or conspicuously 2-lipped, with upper lip 3-toothed and lower lip 2-toothed. Corolla white, yellow, or purple-red, 2-lipped; tube dilated in front near base, long exserted, not hairy annulate inside; upper lip short, straight, margin entire or emarginate; lower lip longer, subpatent, 3-lobed; middle lobe largest, emarginate, margin undulate to dentate. Stamens 4, ascending beneath upper corolla lip; filaments complanate, puberulent; anthers with 2-locular, bearded pollen sacs. Ovary glabrous. Style 2-cleft, lobes subulate. Nutlets flattened dorsiventrally, obliquely long winged at apex.
About 16 species: Asia, 13 species in China.