Shrubs or subshrubs, (15-)25-30(-50+) cm. Stems pannose (white). Heads borne singly. Peduncles 35-60(-80+) mm. Involucres 6-8 mm. Rays 3-6; laminae (8-)12-20 mm, spreading to reflexed in fruit. Disc florets (6-)10-17(-25). Cypselae usually glabrous, sometimes gland-dotted; pappi of 4-6 oblong to ± lanceolate scales 2-2.5 mm. 2n = 32.

Flowering (Feb-)Apr-Jun(-Dec). Creosote-bush scrub, sandy washes; 100-2100 m; Ariz., Calif., Nev., Utah; Mexico (Baja California, Sonora).

Duration: Perennial

Nativity: Native

Lifeform: Subshrub

General: Suffrutescent perennial, few to many stemmed clumps 25-30 cm tall, stems and leaves densely white tomentose.

Leaves: Alternate, linear, 1-4 mm wide, 2-10 cm long, green and glabrous with age, midrib conspicuous with age.

Flowers: Heads borne singly at the tips of branches on peduncles 2-10 cm long, involucres campanulate 6-8 mm, phyllaries 5-12 in 1-2 series; ray florets 3-8, pistillate, rays 12-20 mm, spreading to reflexed in fruit, pale yellow, coarsely 3-toothed, papery; 10-17 disc flowers exserted 3-4 mm beyond involucre at anthesis.

Fruits: Glabrous cypselae, sometimes gland-dotted, pappi of 4-6 oblong to lanceolate scales 2-2.5 mm.

Ecology: Found along washes, on gravelly slopes and rocky hillsides from 2,000-5,000 ft (610-1524 m); flowers March-September.

Distribution: s UT, s NV, s CA, AZ, w NM; south to nw MEX.

Notes: The most suffrutescent of the Psilostrophe in the region, as well as having the most tomentose herbage. Pay attention to the exserted disc flowers to distinguish between Psilostrophe, Zinnia, and Melampodium.

Ethnobotany: Unknown, but other species in the genus have many uses.

Etymology: Psilostrophe is from Greek psilos, naked or glabrous, and strophe, to turn, while cooperi is named for Dr. James Graham Cooper (1830-1902) an American geologist who collected plants in the Mojave in 1861.

Synonyms: Riddellia cooperi

Editor: SBuckley, 2010