Centaurea thuillieri

Centaurea thuillieri is a herbaceous perennial of the Asteraceae family belonging to the brown knapweed (Centaurea jacea) species complex of Europe, often treated as a subspecies of C. jacea or as a stabilised hybrid between C. jacea and C. nigra. Plants are 20 to 100 centimetres tall, with single or sparingly branched, erect, angular and rough hairy stems arising from a stout crown. Basal leaves are ovate to lanceolate, sometimes shallowly pinnately lobed and gradually narrowing into a winged petiole; stem leaves are smaller, sessile, lanceolate to linear-lanceolate with entire margins. From June to October the stems carry solitary terminal flower heads 2 to 6 centimetres across, composed of all tubular flowers; the central disc florets are deep violet-purple, and the marginal florets are enlarged, sterile and ray-like in appearance. The involucre is ovoid with overlapping bracts that bear a rounded, entire-edged or shortly crested, pale brown to dark brown papery appendage — a key feature distinguishing the species from neighbouring members of the complex. The fruit is a small, shiny, obovate achene about 3 millimetres long lacking a pappus. It grows in dry to mesic grassland, meadows and open woodland edges across western and central Europe.