Mostly perennial, rarely biennial herbs or shrubs, with erect or ± prostrate stem. Leaves opposite, or in whorls, petiolate or sessile, mostly ovate or ovate-lanceolate; stipules divided in 2-setaceous lobes. Inflorescence terminal or axillary corymb, often somewhat spicate. Flowers hermaphrodite, often di- or trimorphic. Calyx tube globose or ovoid, mostly adnate to the ovary, 5 (-6-lobed, lobes often foliaceous, subpersistent in fruit; stipitate glands present between each pair of calyx lobes. Corolla-tube long, hairy, dilated at the throat, throat hirsute inside; lobes 5-6, ovate or oblong, valvate. Stamens 4-6, exserted, filaments short. Anthers dorsifixed. Ovary 2-loculed; ovules numerous; style branched, hairy, filiform, included; stigma papillose. Fruit 2-loculed, many-seeded capsule, obtriangular or ovoid, ribbed, beaked, opening at apex, splitting into 4 valves, externally papillate. Seeds minute, brownish, irregular, globose or tetrahedral, testa reticulate.