Description from Flora of China
Herbs, subshrubs, or shrubs. Verticillasters in continuous or interrupted spikes or capitula; spikes cylindric or secund, often compact, sometimes in panicles; bracts ovate or flabellate to minute, narrower than calyx. Calyx campanulate or cylindric, throat glabrous; teeth 5, subequal or anterior 2 longer. Corolla white, yellowish, or purplish, 2-lipped, hairy and glandular outside, hairy annulate or glabrous inside; tube to slightly longer than calyx, straight or slightly curved, funnelform; upper lip straight, margin entire or emarginate; lower lip spreading, 3-lobed, lateral lobes entire; middle lobe largest, margin entire, apex erose or emarginate. Stamens 4, usually exserted, anterior 2 longer, rarely undeveloped, free; filaments glabrous; anther cells 2, divergent or divaricate, apex confluent. Ovary glabrous. Style usually exserted beyond stamens, apex deeply to shallowly 2-cleft; lobes subulate, sublinear or clavate, usually equal. Nutlets ovoid to oblong, glabrous or sparsely hairy, tuberculate or smooth.
About 40 species: Europe, Japan, Korea, North America; 33 species in China.