Description from Flora of China
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)