w00dyphyl's picture


Observed: 27th July 2012 By: w00dyphylw00dyphyl’s reputation in Plantsw00dyphyl’s reputation in Plantsw00dyphyl’s reputation in Plants
Species interactions

No interactions present.

Species with which Common Knapweed (Centaurea nigra) interacts


lavateraguy's picture

The taxonomy of the ...

... Centaurea jacea group is difficult, but some pseudoradiate knapweeds are assigned to Centaurea debauxii.

The shape of the phyllaries (bracts) is a useful character for distinguishing Centaurea, but isn't particularly helpful with nigra/jacea/debauxii. It does however easily distingish these from scabiosa.

Mark at Magdalen's picture


In mainland Europe they’re certainly more species of knapweeds and identification can be tricky.

In Britain you are only likely to come across two, common and greater knapweed.
Common knapweed is certainly a variable plant. Some populations have distinctly swollen tops to their stems whilst others (often called lesser knapweed) are more slender with virtually no swelling behind the flower head. In addition both forms can be found with rayed and un-rayed flower heads. The taxonomic status of these forms is a matter of some debate and has been for many years. Recently Centaurea debeauxii (Chalk Knapweed) has been given full species status and is recognised as a native plants but I think identification is rather tricky and probably best left to experts.

I think your photo is of common knapweed. Greater knapweed which is always rayed, can look a little like the rayed form of Common knapweed but can be told apart by the following features. In Common knapweed the bracts that make up the ‘hard head’ are pale brown with black/brown bristly edges. However the degree of overlap obscures most of the pale brown. In Greater knapweed these bracts are grey-green with black/brown bristly edges but, because there is less overlapping, much of the bract is still visible. In Common knapweed the leaves of the upper stem are lanceolate and in Greater knapweed they are toothed.

A photo taken side on would be useful.