Perennials (sometimes flowering first year), (20-)90-200 cm. Stems 1 (from rhizomes) or 2-3+ (from caudices), usually erect (sometimes relatively thick), branched mostly distally (usually relatively leafy proximally, sometimes sparsely leafy distally), glabrous or sparsely arachnose to tomentose. Cauline leaves: proximal (somewhat thick, usually withering early) elliptic, oblanceolate, lanceolate, or linear (sometimes 1-2-pinnately lobed, lobes lanceolate or linear to filiform, sometimes antrorse, bases usually tapering), ultimate margins entire or dentate to denticulate, faces glabrous or ± arachnose to tomentose; distal reduced. Calyculi of 12-18(-30), lanceolate to subulate bractlets, hyaline margins 0.05-0.2 mm. Involucres ± campanulate, 9-12(-16+) × 6-8(-12+) mm. Phyllaries 18-30+ in 2-3 series, lanceolate or linear to subulate, hyaline margins 0.05-0.2 mm wide, faces glabrous or ± arachnose and glabrescent. Receptacles not bristly. Florets 41-100; corollas white (usually each with abaxial purple stripe), 13-20 mm; outer ligules exserted 8-14 mm. Cypselae ± prismatic, 1.4-2.5 mm, ribs extending to apices (± muriculate at 30×), 5 more prominent than others; pappi persistent, of fimbriate crowns or 20-25, blunt teeth (0.01-0.1 mm). Pollen 70-100% 3-porate. 2n = 18.
The Malacothrix saxatilis complex is taxonomically difficult. The varieties intergrade morphologically in leaf shape, indument, blooming time, and growth cycle, depending on relative habitat conditions such as elevation, soil, and temperature regime. Hybridization may occur between varieties where they are sympatric. In addition, arrays of heads in early bloom may be described as congested (peduncles relatively short) and as open (peduncles relatively long) on the same plant at the end of the season.
Varieties commutata, arachnoidea, and saxatilis are similar in leaf morphology; var. arachnoidea is distinguished from var. commutata mainly by its tomentose herbage; var. saxatilis differs from the other two varieties in minor details of leaf morphology and in its area of distribution; var. implicata is the most distinctive variety; and var. tenuifolia differs from the others primarily in cauline leaf morphology, which is quite variable. Variety altissima has been described as similar to vars. arachnoidea and commutata and different from vars. saxatilis, implicata, and tenuifolia in growth habit. It is similar in leaf morphology to var. tenuifolia but differs from vars. arachnoidea, commutata, implicata, and saxatilis. Here, var. altissima is subsumed in var. tenuifolia.
