*Centaurea calcitrapa
Corollas purple. Pappus absent. Involucral bracts horny, with a spreading spine 1–2 mm long. Leaves pinnatifid, with a few long linear or lanceolate lobes. Heads sessile in the forks or within the last leaves of the branches. Cypselas 2 mm long. Erect annual up to 25 cm high, usually with a cottony down. Widespread. Weed of cultivation and waste places. Introd. from the Mediterranean. Fl. summer. Star Thistle