Plants 5-25(-35) cm; proximal indument grayish, arachnoid-sericeous to closely lanuginose (sometimes tardily glabrescent). Stems mostly 1-5; branches mainly proximal. Leaves basal (withering) and cauline, 1.5-7 cm; largest blades ± elliptic to ovate, ± plane, not succulent, 1(-2)-pinnately lobed (± gland-dotted beneath indument); primary lobes mostly 2-5 pairs, ± remote, ultimate lobes ± plane. Heads (± radiant, nocturnally), mostly 1-5(-7) per stem (nodding in bud). Peduncles 1.5-8 cm, arachnoid-sericeous to thinly lanuginose distally, not stipitate-glandular. Involucres ± obconic to broadly cylindric. Phyllaries: longest 12-18 mm; outer arachnoid-sericeous to thinly lanuginose in fruit, not stipitate-glandular, apices ± squarrose, blunt, pliant. Florets: corollas (nocturnal) white to pinkish or cream, 9-12(-15) mm (lengths 1.8-2.2 times cypselae; anthers ± included); peripheral corollas nocturnally spreading, actinomorphic, scarcely enlarged. Cypselae 5-6(-7) mm; pappi of 8 scales in 2, abruptly unequal series, longest scales 5-7 mm. 2n = 12.
Flowering Mar-early Jul. Open, loose, light-colored, silty, usually calcareous or alkaline, desert soils, often covered by or mixed with gravel; 600-2200 m; Ariz., Calif., Idaho, Nev., Oreg., Utah.
Though the derived floral features of Chaenactis macrantha obscure its relationships, it may represent a link between sect. Chaenactis (annuals; pappus scales in regular, often strongly reduced series) and sect. Macrocarphus (leaf blades gland-dotted). Resemblance of its heads, leaves, and indument to those of C. thompsonii and relatives is striking. It appears to form no natural hybrids, perhaps because of its nocturnal corollas.