Despite the reduction in flower number, primary capitula in such a syncephalium retain their individual involucral bracts, an indication of their true nature.
In Echinops, the first sign of this basipetal differentiation is the production of involucral bracts subtending each single-flowered primary capitulum (Leins & Gemmeke, 1979).
This meristem will soon differentiate into a one-flowered primary capitulum, complete with involucral bracts.
Involucral bracts linear-lanceolate, acute, [+ or -] 1 mm wide; with stellate, glandular and simple eglandular trichomes in more or less similar proportions.
One of them must have stellate trichomes also on adaxial surface of leaves, stolons absent or, if present, scarce, short and relatively thick and thin involucral bracts with abundant and dominant long simple eglandular trichomes and more or less abundant stellate trichomes: in this area it can only again be P.
argyrolegionensis differs from both of them basically by the involucral bracts and apex of scapes with abundant black glandular trichomes due to the influence of P.
The other species must have scarce, short or not very long and stout stolons with leaves similar than those of the rosette, thicker scapes and capitula, and wider involucral bracts with dominant long simple eglandular trichomes: in this area it can only be P.
argyrocoma because it is more robust, with thicker scapes and capitula, wider involucral bracts, larger leaves of the stolons, among other characters.