Dull green, branched, erect perennial with a stout taproot. Stems hollow, striate, 1-3 m high. Basal lvs entire, linear, apetiolate, up to 1.5 m long × 5 cm at base; margins with small appressed spines 2-5 mm long; stem lvs similar to basal but reduced. Infl. much-branched; capitula numerous, ovoid to ovoid-cylindric, pedunculate, purplish, 5-8-(10) mm long; bracts and bracteoles entire, ovate-triangular, not exceeding fls in fresh material, 1-2 mm long. Fls numerous, purple-tinged, c. 2 mm diam.; calyx teeth ovate, c. 1 mm long. Fr. scaly, 1-3 mm long.