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.

Plant: Perennialherb; STEMS purplish, rather closely to sparingly prickly throughout

Leaves: prickly mainly on the vein, less so above, essentially smooth between the veins; lower and middle cauline leaves lobed one-half to five-sixths to the midrib, the lobes one to two times as long as wide, the margin angular at the apex, the sinuses and lobes subequal in width; uppermost leaves either not clasping or subclasping

INFLORESCENCE: cymose

Flowers: buds subspherical to obovate; calyx with few to many perpendicular prickles per sepal, the sepal horn 6-10 mm long, flattened or angular in cross-section when fresh, the apical prickle usually flattened and indurated at its base; petals white; stamens 150 or more

Fruit: capsules ovate to elliptic, sparsely to closely prickly; SEEDS numerous, pitted

Misc: Dry gravelly soil, foothills, mountain valleys, and high plains; 750-2300 m (2500-7500 ft);; Apr

REFERENCES: Ownbey, Gerald B., Jeffrey W. Brasher, and Curtis Clark. 1998 Papaveraceae. J. Ariz. - Nev. Acad. Sci. 30(2): 120.

Duration: Perennial

Nativity: Native

Lifeform: Forb/Herb

General: Stems purplish, rather closely to sparingly prickly throughout, 50-120 cm tall.

Leaves: Prickly mainly on vein, less so above, essentially smooth between the veins; lower and middle cauline leaves lobed one-half to five-sixths to the midrib, the lobes one to two times as wide, the margin angular at the apex, the sinuses and lobes subequal in width, uppermost leaves either not clasping or subclasping.

Flowers: Buds subspherical to obovate; calyx with few to many perpendicular prickles per sepal, the sepal horn 6-10 mm long, flattened or angular in cross-section when fresh, the apical prickle usually flattened and indurated at its base; petals white, stamens 150 or more.

Fruits: Ovate to elliptic capsule, sparsely to closely prickly.

Ecology: Found on dry gravelly soil, foothills and mountain valleys from 2,500-7,500 ft (762-2286 m); flowers April.

Distribution: AZ, NM; south to n MEX.

Notes: The primary Argemone in the area and very distinct with its prickles all over, showy white petals and many bright yellow stamens followed by globose fruits which emit a black tar when punctured.Two subspecies found in the region subsp. pleiacantha and subsp. ambigua, subsp. pleiacantha is much more prickly than subsp. ambigua.

Ethnobotany: Unknown for this species, but many other uses for species in this genus.

Etymology: Argemone from Greek argemos, a white spot (cataract) on the eye, what it was supposed to cure, pleiacantha is from Greek pleios, many, more than one and akantha, thorn.

Synonyms: None

Editor: SBuckley 2010, FSCoburn 2015