Description from Flora of China
Herbs perennial. Leaves petiolate, ovate, margin serrate. Verticillasters axillary; bracts leaflike, smaller than leaves; bracteoles minute. Calyx campanulate, pendulous after anthesis, 13-veined, ± hairy, 2-lipped, upper lip shallowly 3-toothed, lower lip strongly 2-toothed. Corolla white, yellow-white, yellow, or reddish, 2-lipped; tube included or slightly exserted, slightly dilated at throat; upper lip straight, apex emarginate or 2-lobed; lower lip spreading, 3-lobed, with middle lobe entire or emarginate, wider than lateral lobes. Stamens 4, anterior 2 longer, clinging to upper corolla lip, included or slightly exserted; filaments arcuate; anther cells 2, initially divergent at nearly a right angle, becoming divaricate. Style apex equally 2-cleft; lobes subulate, revolute. Nutlets ovoid, smooth.
About four species: Asia, Europe; three indigenous and one cultivated in China.