Annual rosetted herbs, usually developing elongate stems; indumentum of spreading or antrorsely appressed hairs. Rosette leaves opposite, clustered, petiolate, sheathing at base; cauline leaves alternate, sessile or shortly petiolate. Inflorescences terminal, of simple elongated monochasial scorpioid cymes; bracts present. Flowers distant, pedicellate; sepals 5(–9), partly connate, elongating with age; corolla regular, 5-lobed, more or less cylindric, glabrous, white; stamens included in corolla-tube, anthers more or less sessile; ovary 2–4-lobed, 2–4-celled, style short, inserted near base of ovary; stigma capitate. Fruit splitting into 2–4 mericarps, leaving a conical gynobase; mericarps ovoid, tapering to an apical point, ridged, rugose-tuberculate.
About 100 species, mostly in western North and South America; 5 species in Australia (1 naturalized).