Centaurea nigra subsp. nigra

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 : 293

(a) Subsp. nigra :

Leaves glabrous, green; lower elliptical to ovate-lanceolate. Appendages broadly ovate-triangular,covering bracts, the fimbriae as long as or somewhat longer than width of appendage, 15-20 on each side, dark brown. Outer florets not radiate. 2« = 22. Throughout the range of the species except Portugal.