Description from Flora of China
Herbs annual or perennial, aromatic, often rhizomatous or stoloniferous. Upper leaves sessile or subsessile; blade margin dentate, serrate, or crenate. Verticillasters (2-6)- to many flowered; floral leaves similar to stem leaves or reduced; bracts lanceolate to linear, ± distinct. Flowers bisexual or pistillate. Calyx funnelform to campanulate, 10-13-veined, throat glabrous or hairy, limb equally 5-toothed or 2-lipped, upper lip 3-toothed, lower lip 2-toothed. Corolla funnelform, ± regular or slightly irregular; tube generally included, throat slightly dilated or saccate in front, limb 4-lobed; lobes equal, entire, upper lobe slightly wider, emarginate or 2-lobulate. Stamens 4, subequal, divaricate, erect, exserted in bisexual flowers, included and often rudimentary in pistillate flowers, posterior 2 slightly longer than anterior 2; filaments glabrous; anther cells 2, parallel. Style exserted, apex equally 2-cleft. Nutlets ovoid, dry, smooth or slightly tuberculate, apex rounded, rarely hairy.
About 30 species: mainly in north temperate regions, a few in the Southern Hemisphere; six native and six cultivated species in China.
A number of species are widely cultivated for their aromatic properties and many cultivars have been developed.