Perennial, mostly 60–90 cm high, dioecious, extensively rhizomatous; often unbranched below inflorescences, stems wingless, cobwebbed to glabrescent. Leaves with spiny margins, dark green above, white-tomentose below; basal leaves oblanceolate, to 10 cm long, 4 cm wide, sinuate to dentate, obscurely petiolate; cauline leaves oblanceolate to lanceolate, 1–7 cm long, to 2 cm wide, pinnatifid, base subamplexicaul to somewhat decurrent. Capitula pedunculate, many in loose corymbs, globose to ovoid, 8–15 mm diam.; involucre 8–25 mm long; intermediate bracts lanceolate, erect to slightly spreading, with a broad terminal spine to c. 1 mm long, purple-tipped; inner bracts longer and narrower, acute. Florets unisexual; corolla 12–18 mm long, pale mauve. Cypselas 2.5–4 mm long, pale brown to olive green, finely grooved; pappus 2–2.5 cm long. Flowers mostly Dec.–Mar.