Annuals. Stems branched basally and distally, 2-9 dm. Basal leaves: petiole 0.5-2 cm; blade linear to linear-lanceolate, (2-)3-6(-8) cm × (2-)3-5(-8) mm, base attenuate, margins pinnatifid. Cauline leaves (distal) shortly petiolate or subsessile; blade linear to narrowly lanceolate, base cuneate, margins pinnately lobed. Fruiting pedicels divaricate to slightly reflexed, (8-)10-17(-22) mm, (straight). Flowers: sepals 2-3 × 1-1.5 mm, pubescent abaxially; petals white, (3.5-) 4-6.5 × 2-3.5 mm, attenuate to claw, claw 1-1.5 mm, expanded basally; filaments white, 2-3 mm; anthers 0.8-1.1 mm. Fruits: each valve orbicular, 5-6.5 × 6-7 mm (nearly as long as wide), base and apex rounded, not margined beyond indurated part surrounding seeds, pubescent; style 0.5-1 mm. Seeds suborbicular, 2.5-3.5 × 2-3 mm. 2n = 18.

Flowering Mar-Apr. Sandy hills and flats; 100-800 m; Ariz.; Mexico (Sonora).

Dimorphocarpa pinnatifida is known from Pima and Yuma counties.