Perennial herbs or shrubs, erect, ascending or diffuse, pilose, hirtellous or variously pubescent. Stems branching, often lax, more or less hexagonal in cross-section. Leaves petiolate; blades entire, or undulate, lanceolate to ovate. Flowers sessile, solitary or clustered in contracted cymes, these forming erect, secund, often lax spikes or panicles; bracts 2, frequently small, orbicular to spathulate; bracteoles 2 or 4, opposite in pairs and forming an involucre, outer pair larger than inner, appressed, lanceolate or ovate. Calyx deeply 5-parted, lobes linear-setaceous, equal to subequal, hyaline; corolla red, violet, blue, pink, or white, often resupinate, tube narrow, slightly ampliate, limb nearly regular or more often 2-lipped, upper lip entire, emarginate or 2-toothed, flat or concave, lower lip spreading, slightly 3-lobed; stamens 2, exserted but shorter than upper lip, filaments pubescent in lower half, anthers 2-thecous, thecae often unequal, muticous or longer ones sometimes spurred, staminodes absent; disk cupular, oblique-truncate or sinuate-dentate; ovary with 2 ovules per locule. Capsules ovoid to suborbicular, subsessile, contracted into a short, solid stipe, retinacula separating from inner capsule wall at maturity and protruding prominently from each valve of capsule, mature capsule conspicuously ruptured near base of head; seeds 4 or 2(-1) by abortion, lenticular, with smooth, muricate or squamose surface.
East Indies present, Guianas present, South Africa present, tropical S America present, tropics, subtropics and warm-temperate regions of the world present
Large, taxonomically complex genus of about 150 species in the tropics, subtropics and warm-temperate regions of the world, best developed in the East Indies, South Africa and tropical S America; in the Guianas 4 species.