Plants annual or perennial. Stems branched, 5-12 dm, sparingly to closely prickly. Leaf blades: abaxial surface sparingly prickly on veins, adaxial surface unarmed or sparingly prickly on veins, apices of lobes angular, marginal teeth prominent; proximal lobed ca. 3/4 distance to midrib; distal sometimes clasping. Inflorescences: buds oblong-obovoid or subglobose, body 14-20 × 11-18 mm, prickly, prickles simple or branched; sepal horns terete or adaxially flattened, 4-12 mm. Flowers 8-12(-16) cm broad; petals white; stamens ca. 150; filaments pale yellow to red; pistil 3-4-carpellate. Capsules ovoid to ellipsoid-lanceoloid, 25-45 × 10-16 mm (including stigma and excluding prickles), closely to sparingly prickly, longest prickles 4-6(-8) mm. Seeds 2-2.5 mm.

Lower Taxa

• Argemone pleiacantha subsp. ambigua G. B. Ownbey
• Argemone pleiacantha subsp. pinnatisecta G. B. Ownbey
• Argemone pleiacantha subsp. pleiacantha