Centaurea L.
Involucral bracts terminating in spines Centaurea
Corollas yellow
Heads solitary. Involucral bracts with a spine 2–3 cm long, spinules palmately arranged. Basal leaves lyrate, up to 10 cm long; cauline leaves linear, decurrent, entire. Involucre urn-shaped, 1 cm diam. Cypselas compressed, brown, 2–3 mm long. Pappus bristles 5 mm long. Erect, white-tomentose annual up to 60 cm high. Widespread. Weed of cultivation, pastures and waste places. Introd. from the Mediterranean. Fl. chiefly summer. St Barnaby’s Thistle Centaurea solstitialis
Heads sometimes clustered. Bracts with a spine less than 1 cm long, spinules pinnately arranged. Basal leaves pinnately divided; cauline leaves narrow, decurrent, entire or slightly toothed. Involucre more than 1 cm diam. Cypselas 3–4 mm long. Pappus of bristles up to 5 mm long. Erect annual up to 50 cm high, woolly or glabrous. Widespread. Weed of cultivation, pastures and waste places. Introd. from the Mediterranean. Fl. summer. Maltese Cockspur Centaurea melitensis