Centaurea nigra Common Knapweed

A common, colourful member of mesotrophic grassland communities such as neutral grasslands (e.g. MG5 hay meadows) and roadside verges (MG1) where it is a valuable resource for pollinators. It is found throughout West Glamorgan but is most common in the lowlands. Forms with showy (pseudo-radiate) florets have been called Centaurea nigra ssp. rivularis.

 Common Knapweed, in the broadest sense, is a very familar wild plant in the Welsh countryside and plants identified as such in early editions of Stace's flora, would have been named as either Centaurea nigra ssp. nigra or Centaurea nigra ssp.nemoralis. However the most recent editions of Stace elevate Centaurea nigra ssp. nemoralis to species rank as Centaurea debeauxii (Chalk Knapweed). Furthermore, both have the same number of chromosomes (2n = 44) and will hybridise and intermediates between them are common. At present, we don't have enough, systematic, field data to resolve these taxa (or their intermediates) in a meaningful way and their exact status in West Glamorgan is largely unknown. What we call Centaurea nigra here is an aggregate name that includes all these forms which might be better referred to as Centaurea nigra sensu lato or Centaurea nigra agg.

Helpful descriptions and discussions of Centaurea nigra and Centaurea debeauxii can be found in the paper by M. Harris (2017) in the New Journal of Botany, Volume 2, 169-181 and in an article by Nevil Hutchinson (2023) on the Sussex Botanical Recording Society website (sussexflora.org.uk).