Description from Flora of China
Herbs, subshrubs, or shrubs, erect. Leaves dentate. Bracts subulate to spinescent. Flowers in capitula, compact spikes, or loose panicles. Calyx tubular-campanulate to tubular, erect to oblique, 10-veined, throat tufted villous or glabrous; teeth 5, subequal, straight; fruiting calyx dilated. Corolla 2-lipped; tube cylindric to swollen on 1 side, nearly cylindric to narrowly funnelform; upper lip 2-lobed, lobes erect, spreading, or reflexed; lower lip 3-lobed, middle lobe saccate, reflexed in flower, base constricted, sometimes with projected teeth; lateral lobes similar, conspicuous, close together to lobes of upper lip or to middle lobe. Stamens 4, anterior 2 longer, declined; filaments free, edentate; anther cells 2, apically confluent. Style apex 2-cleft or subentire. Disc entire or slightly swollen in front. Nutlets ovoid to oblong, smooth or dotted, scabrid, membranous winged in a few species.
Some 350-400 species: tropical and subtropical regions of the New World, four naturalized species in China.