Barneby’s thistle

Perennials, 30–50 cm; caudices and woody taproots. Stems 1–few, erect, gray-tomentose or glabrate; branches few, above middle, ascending. Leaves: blades oblong-elliptic, 10–35 × 2–7 cm, strongly undulate, margins shallowly to deeply lobed, lobes 8–15 pairs, linear-lanceolate to broadly triangular, closely spaced, spreading, coarsely spinose-dentate or cleft into 2–5 spine-tipped divisions, main spines 3–5 mm, faces densely gray-white-tomentose; basal usually present at flowering, winged-petiolate; principal cauline becoming sessile and progressively reduced distally, bases decurrent as spiny wings to 5 cm; distal cauline usually much reduced, less lobed. Heads 1–20+, borne singly or clustered at branch tips, in leafy, ± corymbiform arrays. Peduncles 0–4 cm. Involucres ovoid to hemispheric or campanulate, 1.7–2 × 1.5–2 cm, loosely arachnoid on phyllary margins or glabrate. Phyllaries in 6–9 series, imbricate, ovate (outer) to linear-lanceolate (inner), entire, abaxial faces with narrow glutinous ridge; outer and middle appressed, spines ascending to spreading, stramineous, 2–7 mm; apices of inner often flexuous, narrow, flat, entire, spineless, glabrous. Corollas lavender to pink-purple, 18–28 mm, tubes 7–9 mm, throats 4–8 mm, lobes 5–11 mm; style tips 3.5–5 mm. Cypselae tan to brown, 5–5.5 mm, apical collars colored like body, narrow; pappi 15–23 mm.

Flowering summer (Jun–Sep). Dry juniper woodlands, sagebrush scrub, on shale, limestone, sandstone; of conservation concern; 1600–2600 m; Colo., Utah, Wyo.

Cirsium barnebyi occurs from the southern Rocky Mountains of southwestern Wyoming, northeastern Utah, and northwestern Colorado.