Thorne’s thistle

Plants erect, caulescent (rarely nearly acaulescent), 20–130 cm. Stems distally short-branched to openly much-branched throughout, leafy, glabrous or villous with septate trichomes. Leaves: blades oblong, oblanceolate, or narrowly elliptic, usually pinnately lobed more than halfway to midveins, abaxial faces glabrous or gray-tomentose, adaxial glabrous; distal usually deeply divided, fiercely armed with stout spines, the longer 1–3 cm. Heads 1–10+, sessile or pedunculate, solitary or crowded near tip of main stem or branches, usually subtended and ± overtopped by distal leaves. Involucres (broadly ovoid to hemispheric) 2.5–3.5 cm. Phyllaries: outer and mid lanceolate to narrowly ovate, spines slender to stout, 2–8 mm; apices of inner usually abruptly expanded into scarious, erose-toothed appendages. Corollas white to dull purple, 29–34 mm, tubes 14–18 mm, throats 6.5–9 mm, lobes 7–8.5 mm; style tips 5–6.5 mm. Cypselae 4.5–5 mm; pappi 20–27 mm.

Flowering summer (Jun–Sep). Meadows, streamsides, valley bottoms, often in saline soils; 1500–2200 m; Colo., Idaho, Nev., Utah.

Variety thorneae grows mostly in the Basin and Range province of Utah with populations in eastern Nevada, southern Idaho, and western Colorado.