15. Malacothrix sonorae W. S. Davis & P. H. Raven, Madroño. 16: 264, fig. 2d. 1962.
Annuals, 10–35 cm. Stems 1(–9), erect, branched from bases and distally, relatively sparsely leafy, glabrous. Cauline leaves: proximal narrowly oblanceolate to obovate, usually pinnately lobed (lobes oblong to triangular), not fleshy, ultimate margins ± dentate, faces glabrous; distal greatly reduced (margins entire or basally dentate, apices acute). Calyculi of 5–8+, subulate to lanceolate bractlets, hyaline margins 0.05–0.2 mm. Involucres ± campanulate, 6–9 × 4–6.6 mm. Phyllaries 12–15+ in 2(–3) series, lance-oblong to lance-linear, hyaline margins 0.05–0.2 mm wide, faces glabrous. Receptacles not bristly. Florets 30–61; corollas white or pale yellow, 6–10+ mm; outer ligules exserted 1–4 mm. Cypselae ± cylindro-fusiform, 1.7–2 mm, ribs ending 0.2–0.3 mm short of apices, ± equal (distal 0.2–0.3 mm of cypselae slightly expanded, smooth); pappi persistent, of 16–18 needlelike teeth plus 2 bristles. Pollen 70–100% 3-porate. 2. = 14.
Flowering Mar–May. Sandy, open areas among bushes, Larrea-Lycium-Cercidium-Baccharis associations, Quercus, Pinus, Juglans woodlands; 400–1500 m; Ariz., N.Mex.; Mexico (Sonora).
Malacothrix sonorae is found mainly in the Sonoran Desert (Tucson, Kofa, Pinal, White Tank, Baboquivari, and Waterman mountains).