Perennial or rarely annual herbs with trailing or twining stems or, rarely, subshrubs, glabrous or with simple hairs. Leaves simple, entire to deeply lobed, often sagittate or hastate, petiolate. Inflorescences axillary. Flowers solitary or in few-flowered cymes, usually white or pink; bracteoles usually paired, small, distant from calyx; sepals 5, free, equal or subequal; corolla funnel-shaped or campanulate, entire or slightly 5-lobed, distinct hairy (rarely glabrous) mid-petaline bands present; stamens 5, subequal, included, filaments terete above, flattened and dilated below, tuberculate at base; ovary 2-celled, glabrous, ovules 2 per cell, style 1, stigma 2-lobed, lobes linear or oblong. Capsule ovoid or globose, splitting longitudinally into 2–4 valves; seeds 4 per capsule, often verrucose, usually glabrous.
About 250 species, cosmopolitan but mainly from temperate and subtropical regions of the world; 12 species in Australia (11 endemic, 1 naturalized).
Note that in key to species, and in species descriptions, the pedicel is measured from the bracteoles to the calyx and the peduncle from the main stem to the bracteoles, and leaf descirptions are based on mid-stem leaves, i.e. those immediately below the lowest flowers in the inflorescence.