Description from Flora of China
Plants perennial herbs or subshrubs. Leaves mostly linear to oblong, margin entire, involute, or flat. Verticillasters 2- to many flowered, mostly secund, axillary, often in long terminal spikes, lower ones lax, upper crowded; floral leaves similar to stem leaves, reduced; bracts and bracteoles minute. Pedicel distinct. Calyx tubular to subcampanulate, brightly colored, conspicuously 15-veined, hairy, glandular, teeth 5, equal, sinuses with a thickening at junction of 2 side veins. Corolla blue, purple, or occasionally white, hairy outside, glandular, glabrous inside, tube nearly included or conspicuously exserted, limb 2-lipped; upper lip emarginate or 2-lobed, sometimes subentire; lower lip spreading, 3-lobed; middle lobe longer than lateral lobes, truncate to emarginate. Stamens 4, mostly exserted, anterior 2 longer; filaments glabrous; anthers ovoid, cells 2, divaricate. Style apex equally 2-cleft. Nutlets oblong to oblong-ovoid, hairy, glandular, or glabrous.
About 15 species: Africa, Asia, Europe; two native and one cultivated in China.