Centaurea species - Knapweeds and Cornflowers

Stem and leaves are not spiny. Leaves are simple and entire to ±pinnate. Phyllaries have a distinct apical portion which is toothed scarious or spiny.. Lots of aliens and garden escapes.

Centaurea nigra - Common Knapweed leaves entire to deeply lobed, clear midrib, tapering, clear and pale. Flower head, excluding the flowers, mostly 15-20mm across. Peduncles markedly swollen immediately below capitula, central undivided part of each phyllary ovate in shape.

Centaurea debeauxii - Chalk Knapweed like C. nigra except flower head, excluding the flowers, mostly 9-14mm across. Peduncles slightly swollen under capitula, central undivided part of each phyllary lanceolate in shape.

Centaurea montana - Perennial Cornflower Perennial, has basal leaves at time of flowering. All leaves simple and entire. Introduced and often garden escape.

Centaurea cyanus - Cornflower Annual, lower leaves stalked and pinnately lobed, no basal leaves by time of flowering Introduced and often "wild-flower" mix.