Glabrous or pubescent herbs. Stems (plants rarely acaulescent) erect, ascending, or repent, simple or branched, terete or subquadrangular (sometimes winged), glabrous or pubescent. Leaves opposite, usually petiolate; margins entire; without cystoliths. Flowers sessile or short-pedicellate, few or numerous, in terminal or axillary, loose or compact spikes or capitula, spikes sometimes branched at base, lower bracts leaf-like and always opposite, upper ones usually alternate, each bract subtending a single flower with 2 bracteoles; bracteoles about as long as bracts but much narrower. Calyx deeply 5-lobed, posterior lobe oblong, usually conspicuously longer and broader than others, 3-veined, hygroscopic in fruiting stage, recurved in a dry atmosphere, anterior pair usually linear, wider than setaceous lateral pair; corolla usually white, red, purple or yellow, with a cylindrical or funnelform tube, limb subregular or 2-lipped, upper lip 2-lobed and much shorter than 3-lobed lower lip, latter curved inward in bud and overlapped by upper lip; stamens 4, usually included, staminode usually present between posterior pair, anther 2-thecous,theca ovate, subequal, muticous; disk inconspicuous; ovary with numerous ovules in each locule, style filiform, stigma 2- or 3-lobed, lobes unequal. Capsule oblong, obtuse, nonstipitate, seedbearing nearly its entire length, valves with 25-30 seeds, without retinacula; seeds numerous, minute, subglobose, areolate, with mucilaginous trichomes, when moistened, flung away by incurving margin of valve at dispersal.
Africa present, Asia present, Asia-Tropical: Borneo present; Malaya (Peninsular Malaysia present); Sumatera (Sumatera present), Guianas present, Neotropics present, tropical areas of America present
About 80 species in tropical areas of America, Africa and Asia, most abundant in Sumatra, Borneo and the Malay Peninsula; about 26 species in the Neotropics; 6 species occur in the Guianas.