Description from Flora of China
Herbs annual or perennial. Stem leaf blades circular or reniform to ovate-lanceolate, margin coarsely crenate or dentate-serrate. Verticillasters 4-14-flowered; floral leaves similar, much longer than verticillasters; bracts ± linear, early deciduous. Calyx tubular-campanulate to campanulate, 5- or 10-veined, ± hairy outside, throat slightly oblique or regular; teeth 5, subequal, subulate, as long as or longer than tube. Corolla purple-red, reddish, yellowish, to dirty white, 2-lipped, 2(-3) × as long as calyx, hairy outside; tube straight or incurved, cylindric or widened above annulus, subsaccate; upper lip erect, oblong, rounded or emarginate, ± galeate; lower lip spreading, 3-lobed; middle lobe obcordate, emarginate or 2-lobed; lateral lobes semicircular, margin crenate or dentate. Stamens 4, hairy, anterior 2 longer, ascending beneath upper lip; anther cells 2, divaricate. Ovary lobes apically truncate, glabrous or tuberculate, sometimes with a membranous margin. Style apex subequally 2-cleft.
About 40 species: Africa, Asia, Europe, introduced in North America; four species in China.