Description from Flora of China
Herbs, erect or creeping, blackened when dry, villous with eglandular hairs, some with glandular hairs, frequently aromatic. Leaves opposite; leaf blade glandular punctate, margin serrate. Flowers short pedicellate or sessile, in racemes, spikes, or heads, sometimes solitary in axils of apical leaves. Bracteoles 2. Calyx deeply 5-lobed; upper lobe usually large. Corolla tubular; limb 2-lipped; lower lip spreading flat, 3(or 4)-lobed; upper lip erect, emarginate or entire. Stamens 4, didynamous, included; anther locules separate, short stipitate. Style entire or 2-lobed, apex dilated. Capsule ovoid to ellipsoid, septifragal, 4-valved, apex beaked. Seeds numerous, minute; seed coat reticulate.
About 15 species: S and SE Asia, China, Pacific Islands; four species in China.