Shasta Valley thistle

Plants caulescent, 25–70 cm. Stems (1) often very stout, branched distally or throughout, leafy, glabrous, villous with septate trichomes, or arachnoid-tomentose. Leaves oblanceolate to elliptic, deeply pinnately lobed, longer spines slender or stout, usually 1 cm or shorter, abaxial thinly to densely arachnoid-tomentose, villous with septate trichomes along midveins, adaxial villous with septate trichomes or thinly arachnoid-tomentose. Heads 3–many, evidently pedunculate, in corymbiform or subcapitate arrays at stem tips (in age clustered axillary heads sometimes developing), subtended and ± overtopped by distal leaves or these ± reduced. Involucres 2.5–4 cm. P hyllaries: outer and mid lanceolate to ovate, spines slender to ± broad and flat, 1–6 mm; apices of inner linear-acuminate or more commonly expanded as scarious, erose-toothed appendages, often contorted. Corollas white, 30–36 mm, tubes 14–22 mm, throats 7–12 mm, lobes 5–10 mm; style tips 6–8 mm. Cypselae 4–6.5 mm; pappi 22–32 mm.

Flowering summer (Jun–Jul). Wet ground, meadows, pastures, marshes; 900–1900 m; Calif., Oreg.

Variety robustum is known only from northern California (Siskiyou County) and south central Oregon (Klamath and Lake counties). It differs from var. scariosum in its larger, evidently pedunculate heads.