Klamath thistle

Cirsium acanthodontum S. F. Blake; C. oreganum Piper

Phyllaries imbricate or subequal, linear, margins and/or apices regularly spinulose-serrulate, sometimes weakly expanded and scarious. Corollas usually purple (infrequently cream-colored), 20–25 mm, tubes 8–12 mm, throats 5–6 mm, lobes 6–8 mm. 2n = 32.

Flowering late spring–summer (May–Aug). Sea bluffs, river valleys, meadows, grasslands, open coniferous or mixed coniferous-hardwood forests; 10–1200 m; Calif., Oreg.

Plants of var. rivulare occur in the western Klamath Mountains of southwestern Oregon and northwestern California and the adjacent coastal plain. Although these plants are usually slender and erect with well separated leaves, they assume a compact growth form in maritime habitats.