Herbs, annual, biennial, or perennial, usually stout, mostly branched, spiny, bitter yellow lactiferous. Stems mostly erect. Leaves pinnate, lobes repand dentate, teeth apically spiny. Flowers solitary, terminal or arranged in cyme, trimerous; receptacles narrowly conical. Flower buds erect. Sepals (2 or)3, caducous, apex with horned appendices. Petals (4-)6, in 2 whorls, contorted or imbricate in bud, orange, yellow, yellow-white, or white, occasionally pink or mauve. Stamens many, free; filaments filiform or slightly ampliate below middle, apically subulate; anthers linear, nearly basal, bifid, extrorse, curved after dehiscence. Ovary ovoid, conical-ovoid, or nearly elliptic; carpels (3 or)4-6, united; ovules many; styles very short or absent; stigmas as many as carpels, actinomorphic. Capsule spiny, rarely not spiny, apex divided for a short distance into 3-6 valves, rarely parting nearly to base. Seeds many, spheroidal; caruncle very small or absent, seed coat tessellate.

Twenty-nine species: mainly in North America from United States to C Mexico and the West Indies, nine species in South America (three in Chile), one in Hawaii, and the others scattered along the NW and W coasts of the Americas; one species (introduced) in China.

(Authors: Zhang Mingli (张明理); Christopher Grey-Wilson)