Plants perennial. Stems widely branching, 4-8 dm, moderately to copiously prickly throughout. Leaf blades: abaxial surface prickly on main veins, adaxial surface prickly or unarmed on main veins, densely prickly-hispid to glabrous between veins; basal lobed 2/3-4/5 distance to midrib, lobe apices angular, marginal teeth 3 mm or more; distal clasping. Inflorescences: buds subglobose to oblong, body 16-25 × 15-20 mm, prickly; sepal horns angular in cross section, 8-14(-18) mm, apical prickle indurate. Flowers 8-11 cm broad, closely subtended by 1-2 foliaceous bracts; petals white; stamens 150 or more; filaments pale yellow; pistil 4-5-carpellate. Capsules ellipsoid, oblong or lance-ovoid, 25-50 × 10-18 mm (including stigma and excluding prickles); prickles basally herbaceous, spreading or reflexed, unequal, longest branched, 8-15 mm. Seeds 2-2.5 mm.

Subspecies 2 (2 in the flora): w North America.

Lower Taxa

• Argemone squarrosa subsp. glabrata G. B. Ownbey
• Argemone squarrosa subsp. squarrosa