Erect perennial herb to 60 cm high, with short rootstock and clusters of blackish tubers. Basal leaves to 45 cm long, (bi)pinnatisect, segments linear, spine-tipped. Main flowering stem arising from base of the plant, 1–3-branched from a pair of opposite spiny bracts 7–35 cm above ground level and dichotomously or ternately branched from succeeding pairs of bracts, producing a rather rigid dichasial inflorescence, the strongly ribbed flowering stems and flowering heads usually metallic blue; flowering heads c. ovoid, mostly c. 10(–15) mm long, c. 10 mm wide; bracteoles of involucre and apex 15–20 mm long, those subtending flowers conspicuous, exceeding them by 8–15 mm; petals bluish-purple, apex fimbriate. Fruit 4–5 mm long with crowded, thin, long, acuminate vesicular scales Flowers Nov.–Jan.