Annual or perennial herbs, less often trees or shrubs. Leaves opposite or alternate, simple, palmate or pinnate; stipules absent. Inflorescences terminal cymose clusters or dense heads, or flowers solitary in axils. Flowers bisexual, regular or slightly zygomorphic, often showy; bracteoles present or absent; sepals 4 or 5, usually fused into a tube, persistent in fruit; petals 4 or 5, fused into a tube at base, lobes spreading, contorted in bud; stamens 5, inserted on corolla-tube, alternating with lobes, anthers dehiscing by longitudinal slits; ovary superior, usually 3-celled, ovules 1 or more per cell, placentation axile, style filiform, simple, stigma usually 3-lobed. Fruit usually a loculicidal capsule; seeds with endosperm, often sticky when wet.
18 genera with c. 385 species, mainly from North America but also South America, Europe and northern Asia; 4 genera in Australia.