Description from Flora of China
Herbs or subshrubs, with rhizomes or stolons. Stems erect or ascending, simple or branched from base. Leaves simple, petiolate or subsessile, cordate to lanceolate, penniveined. Verticillasters 2-6-flowered, in false spikes, terminal racemes, or panicles of racemes; bracts rhombic-ovate to linear-lanceolate, margin entire or dentate. Calyx 10-veined, throat glabrous to pilose annulate; tube tubular to campanulate, swollen in front at base; limb equally 5-toothed to 2-lipped, upper lip 3-toothed, lower lip 2-toothed. Corolla 1-lipped; tube included or exserted, not hairy annulate inside; limb 5-lobed, with middle lobe circular or spatulate, occasionally 2-lobulate; lateral lobes 4, small. Stamens 4, anterior 2 slightly longer, all exserted from posterior sinus of corolla; anther cells divaricate. Ovary globose. Style equal to or slightly longer than stamens, equally or subequally 2-cleft at apex. Nutlets obovoid, glabrous, smooth to netted, areole ca. 1/2 as long as nutlet.
Approximately 260 species: worldwide, but abundant in the Mediterranean region; 18 species in China.