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Common Knapweed

Black knapweed looks like a thistle but has no prickles; it is closely related to thistles hence the familiarity. That close knit purple flower head is smaller than the more expansive flower of its close cousin, the greater knapweed.

The seed case under the flower head turns hard and black once the petals have died away and that is where its other name, hardhead, comes from.

A very common plant across Dorset.


Common Name Common Knapweed
Alternative Name(s) Black Knapweed
Scientific Name Centaurea nigra
Species Group Daisy Family Compositae
Interest Level
Look for
Identification Notes
Primary Habitat
Family Daisy family - Compositae
Status Locally common
Flower Colour Group Purple
  • 07 - July
  • 08 - August
  • 09 - September
Preferred Environment
Look for Thistle-like flower but without thorns or prickles
Additional Identification Notes
Similar Species

The records for this species have been organised into reports, charts, maps and photos. Click a pic below to see the detail:

Notebook Distribution Map Sites List Some Charts Some Photographs Recent Records Guidance Notes

To see related species click here: 

Daisy Family Compositae