Perennial sometimes annual, suffrutescent, armed or unarmed herbs or shrubs, rarely climbers or small trees. Leaves exstipulate, usually simple, opposite-decussate, entire or undulate-dentate, rarely crenate-dentate or lobed, mostly with cystoliths on the upper surface, petiolate or sessile. Flowers commonly in dichasial cymes becoming monochasial, often in dense to lax spikes, racemes, panicles, sometimes fasciculate or verticilate, rarely solitary; sessile or pedicellate, bisexual, hypogynous, usually zygomorphic; bracts 1,2 or more, often coloured, frequently large, imbricate, persistent, rarely absent. Calyx usually gamosepalous, persistent, 4-5-lobed, lobes valvate or imbricate, sometimes spinescent or reduced to truncate or 10-15-dentate minute tube. Corolla gamopetalous, tube cylindrical or ventricose, the limb of 5, subequally spreading lobes or strongly 2-lipped; upper lip erect or suberect, entire or 2-fid rarely absent or fimbriate; the lower lip more spreading, 3-fid or 3-lobed, lobes imbricate or controrted. Stamens 4 and didynamous or 2, epipetalous, ascending below the upper lip; anthers dorsifixed, usually unequal in a stamen pair, dithecous or monothecous, thecae parallel, divergent or superposed, appendaged or bearded, longitudinally dehiscent; stamindodes 0-1-3. Ovary conical or oblong-cylindric, bicarpellate, syncarpous, superior, sessile or minutely stipitate, bilocular, placentation axile, rarely parietal, ovules 2-10 (-many) in each locule, in 1 or 2 vertical rows, rarely collateral, anatropous; style simple, filiform stigmas 1 or 2 minute. Fruits a bivalved, 2-loculed, clavate to elliptic-ovoid or oblong-cylindric, terete or compressed, usually ± stipitate capsule, elastically dehiscent from apex downwards, rarely drupaceous. Seeds mostly flattened and lenticular or discoid rarely globose or angular, borne on retinacula or papillae, testa smooth, rugose, echinate, tuberculate, glochidiate, appressed hairy or papillate, embryo with scanty or no endosperm.