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Common Knapweed

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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.


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

Sites List Distribution Map Some Charts Some Photographs Original Tweets Relatives Guidance Notes
Common Name Common Knapweed
Alternative Name(s) Black Knapweed
Scientific Name Centaurea nigra
Family Daisy family - Compositae
Status Locally common
Interest Level
Species Family Daisy Family - Compositae
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

This species is often found in these habitats:

Habitat(s) Relationship
GN: Neutral Grassland Associated