Centaurea solstitialis subsp. solstitialis, Asso, 1779

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1976, Flora Europaea. Volume 4. Plantaginaceae to Compositae (and Rubiaceae), Cambridge University Press : 284

(a) Subsp. solstitialis :

Appendages erect or slightly deflexed, with 3-5(-7) yellowish spines, the apical stouter and longer than the others. Almost throughout the range of the species.