Centaurea nigrescens subsp. nigrescens

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 : 292

(a) Subsp. nigrescens ( C. vochinensis Bernh. ex Reichenb. ): Stems branched. Cauline leaves ovate-lanceolate, attenuate at the base, entire or with few teeth. Involucre (9—)10—11 mm in diameter, ovoid-cylindrical. Outer florets not radiate. From S. Germany to Romania and Bulgaria, but only north and east of the Alps.