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Subspecies twisselmannii is found only in the El Paso and Rand mountains of the western Mojave Desert. Subspecies covillei is more widespread across the northern Mojave, and ssp. minutiflora extends north into the Great Basin, south to Baja California Sur and Sonora, and east to Arizona.
PLANT annual, 0.5-3.5 dm tall, erect or spreading, glaucous. LEAVES basal and cauline, terminal divisions obtuse. INFLORESCENCE cymose or solitary. FLOWERS nodding in bud; receptacle conic; calyx short-pointed, glaucous or glabrous; petals 0.3-2.6 cm long, yellow, sometimes with orange spot at base. FRUITS 3-6 cm long. SEEDS 1-1.4 mm diam, ellipsoidal, reticulate, brown to black. Desert washes, flats, and slopes; 0-2000 m. DSon, DMoj, SNE; w AZ, s NV, sw UT, nw Mex. The typical form is hexaploid (2n=36), with petals 0.3-1.0 cm long. The tetraploid (2n=24) of c and n DMoj with petals 0.6-1.8 cm long is subsp. covillei (E. Greene) C. Clark. The diploid (2n=12), rare in the El Paso and Rand Mtns of extreme w DMoj with petals 1.0-2.6 cm long is subsp. twisselmannii C. Clark & Faull.
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