Plants perennial. Stems 4-12(-18) dm, moderately prickly throughout, prickles patent, longest 7-10 mm. Leaf blades: abaxial surface prickly on main veins, adaxial surface unarmed or sparingly prickly on midrib; basal blades shallowly to often deeply lobed; distal not clasping. Inflorescences: buds subglobose to oblong, body 15-18 × 12-15 mm, sparingly prickly, prickles patent; sepal horns usually slender, terete, (5-)8-12(-14) mm, unarmed or with 1-2 prickles near base. Flowers 6-9 cm broad; petals white; stamens about 150; filaments pale yellow; pistil 3-4-carpellate. Capsules narrowly ellipsoid to narrowly ellipsoid-ovoid, 30-45 × 8-14 mm (including stigma and excluding prickles), scattered-prickly, surface clearly visible, longest prickles 6-8(-10) mm. Seeds to 2 mm. 2 n = 28.

Flowering spring; fruiting spring-summer. Washes and outwash plains, deserts; 0-900 m (s to n); Ariz.; Mexico (Sonora and Baja California).