Mem. Torrey Bot. Club 21: 53. 1958.
Plants annual or biennial. Stems widely branching, to ca. 8 dm, prickly throughout. Leaf blades: abaxial surface sparingly to copiously prickly on and sometimes between veins, adaxial surface less so; proximal lobed 5/6 distance to midrib; distal often clasping. Inflorescences: buds oblong, body 18-25 × 14-18 mm, prickly, longest prickles sometimes branched; sepal horns angular in cross section or flattened, 8-12 mm, prickly, apical prickle indurate. Flowers 8-12 cm broad, closely subtended by 1-2 foliaceous bracts; petals white; stamens 150 or more; filaments pale yellow; pistil 5-6-carpellate. Capsules ovoid, 40-50 × 15-25 mm (including stigma and excluding prickles); prickles herbaceous, erect or reflexed, often branched, very unequal, longest 15-35 mm. Seeds 2.5-3 mm. 2n = 84.
Phenology: Flowering spring–summer; fruiting summer–fall.
Habitat: Fields, pastures, hills
Elevation: 150-500 m (transition zone between lowlands and plateau)