Perennial or annual herbs or subshrubs, gland-dotted. Leaves opposite or in whorls of 3 or 4, or sometimes becoming alternate towards inflorescence, simple, sessile. Inflorescence racemose, slender, sometimes dense, flowers single or clustered in the bract axils; bracteoles 2, appressed to the calyx. Sepals 5, free; corolla 2-lipped, tube not swollen or spurred, symmetrical at base, upper lip 2-lobed, recurved, lower lip 3-lobed, without a palate; stamens 4, in pairs of unequal length, anthers of each pair joined, each with 2 stipitate locules, filaments without spurs; stigma perpendicular to style, with 2 equal broad flaps. Capsule septicidal, leaving remnants of the septum attached to the 2–4 valves and completely free from the central column; seeds numerous, not winged.
60 species, mostly tropical, in America, Australia, India and Africa; c. 20 species in Australia, 19 endemic.