Plants 50-250 cm, herbage canescent-tomentose throughout. Stems: wings 0.5-2 cm wide. Leaves 10-50 cm, margins shallowly to ± deeply 1-2-pinnatifid with 8-10 pairs of triangular lobes. Heads mostly borne singly at branch tips. Involucres 30-60 mm diam (excluding spines) ± spheric, bases truncate to concave. Phyllaries lanceolate to ovate, bases 3-8 mm wide, glabrous or ± cobwebby-tomentose, spines to 5 mm. Corollas purple, 25-35 mm. Cypselae 4-5 mm; pappi of many whitish, plumose bristles 10-12 mm. 2n = 34 (France).

Flowering summer (Jun-Aug). Grasslands, fields, roadsides, oak woodlands; 200-500 m; introduced; Calif.; s Europe (Mediterranean region); introduced in Australia.

Illyrian thistle is considered to be a noxious weed in California where efforts to eradicate it from the state´s flora have been implemented. This species has also invaded rangelands in Australia, where it is introduced.