Erect or procumbent, annual or perennial herbs or shrubs with hexagonal stems. Leaves mostly petiolate, ovate or elliptic, entire or somewhat undulate, acute. Flowers of various colours, sessile or subsessile, in axillary or termini cymes, spikes panicles or thyrses; bracts 2-4 pairs, larger than calyx, partially united at the base; bracteoles equalling the calyx, linear or linear-lanceolate. Calyx usually hyaline, 5-lobed, lobes equal, linear-lanceolate. Corolla tube slender, ampliate upwards, not twisted, limb deeply 2-lipped, upper lip erect, entire or emarginate, lower lip larger than the upper, recurved, shallowly 3 lobed. Stamens 2, free, well exserted, anthers bithecous, thecae superpose glabrous, always muticous; staminodes absent. Ovary bilocular, locules 2-ovuled; style filiform with minutely bifid stigma. Fruit an ovoid or suborbicular, ± compressed, subsessile or stipitate, elastically dehiscent 2 or 4-seeded capsule. Seeds flat, ovoid or suborbicular, smooth, muriculate or glochidiate.