Thompson’s pincushion

Perennials, 10–30 cm (not or scarcely cespitose, not matted); proximal indument thinning with age, grayish, arachnoid-sericeous to thinly lanuginose. Stems mostly 5–15+, ascending to erect. Leaves mostly cauline, 2–5 cm; largest blades ± elliptic, ± plane, 1-pinnately lobed; lobes mostly 2–5 pairs, remote, ± plane. Heads mostly 1–3 per stem. Peduncles ascending to erect, 2–5 cm. Involucres ± obconic. Phyllaries: longest (10–)12–15 mm; outer closely lanuginose, not stipitate-glandular, apices erect, ± rigid. Corollas 7–9 mm. Cypselae 7–9 mm (eglandular); pappi: longest scales 3.5–5 mm.

Flowering Jun–Aug. Rocky or gravelly serpentine slopes, scree, talus, openings in or above conifer forests; of conservation concern; (900–)1200–2200 m; Wash.

Chaenactis thompsonii appears to be sister to C. evermannii; it is known from the mountains of central and northwestern Washington. The similar habits of C. thompsonii and C. ramosa (= C. douglasii var. douglasii) appear to result from convergent evolution in the distinctive habitat of their type localities (Wenatchee Mountains), not from a close genetic relationship as suggested by Cronquist.