Annuals or perennials, 50-150 cm (taproots stout). Stems erect or decumbent, sericeo-villous (hairs white). Leaves mostly cauline; mostly alternate; petioles 1.5-3.5 cm; blades deltate or deltate-ovate, 3-7 × 2-4 cm, bases cuneate, margins entire or serrulate, abaxial faces densely sericeous, gland-dotted. Heads 1-3. Peduncles 4-17 cm. Involucres hemispheric, 8-28 mm diam. Phyllaries 18-21, lanceolate, 8-10 × 1-3.5 mm, apices shortly attenuate, abaxial faces densely white-canescent. Paleae 8-11 mm, subentire to 3-toothed. Ray florets 10-13; laminae 16-25 mm. Disc florets 50+; corollas 4.5-6 mm, lobes reddish; anthers brownish red, appendages reddish (style branches reddish). Cypselae 4-8 mm, ± villous; pappi of 2(-3) lanceolate scales 1.5-3 mm plus 2-4 obtuse scales 0.5-1 mm. 2n = 34. Flowering fall-spring. Sand hills; of conservation concern; 50-300 m; Ariz., Calif.; Mexico (Sonora). Subspecies tephrodes differs from subsp. niveus, which is not known to occur north of Mexico, by having less densely hairy phyllaries and generally broader leaves (larger leaves more than 3 cm broad). Both differ from H. petiolaris subsp. canescens (H. niveus subsp. canescens) by lacking the conspicuous white-villous tufts ('beard') of the median cusp of the paleae in the center of the head that characterize H. petiolaris.
Subspecies tephrodes is in the Center for Plant Conservation´s National Collection of Endangered Plants.