Erect, trailing or twining annual or perennial herbs, or erect or scandent shrubs or woody twiners; cystoliths absent. Leaves opposite, entire to crenate or dentate; venation pinnate or palmate. Flowers axillary, solitary or paired or in racemes; bracteoles 2, large, hyaline to leathery, connate for 2/3–3/4 dorsally and about 1/4 ventrally (rarely free to base). Calyx a subentire to undulate rim or with 10–20 triangular to linear teeth. Corolla contorted in bud; tube straight or curved, cylindric or campanulate, widening at point of insertion of stamens, with subsessile capitate glands on the inside; limb spreading, subequally 5-lobed. Stamens 4, didynamous or subequal, inserted at transition from throat to tube, included (rarely exserted); anthers 2-thecous, one or both thecae with a setosely bristled boss or a spur at base (rarely muticous); thecae linear to ovoid, opening by apical slits. Disc conspicuous, annular, fleshy. Ovary 2-locular with 2 collateral ovules per locule; stigma funnel-shaped or with two large unequal lobes (one erect the other horizontal) or subequally 2-lobed with two erect flattened lobes. Fruit a 2–4-seeded thick-walled woody capsule, triangular with weakly defined beak or subglobose with sharply defined beak. Seed hemispherical, hollow on the proximal face, smooth to reticulate, tuberculate, lamellate or otherwise sculptured; retinaculae absent.