Annual or perennial herbs, sometimes lactiferous. Roots and rhizomes often thickened and tuberous. Leaves simple, usually alternate, sometimes opposite, exstipulate. Stems erect, decumbent, trailing or climbing. Flowers usually hermaphrodite, actinomorphic, regular, sometimes cleistogamous. Calyx-tube adnate to the ovary. Sepals with linear to triangular or lanceolate segments. Corolla united, campanulate, infundibuliform or tubular, 5-lobed, sometimes the segments split to the base. Stamens 5 with flattened filaments. Ovary inferior, (2-)3-5 locular, with numerous ovules; styles thick with 3, sometimes 2 stigmas. Fruit a capsule, dehiscing by valves or pores.