Black Knapweed (Centaurea nigra)

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Perennial that grows to heights of 20 – 80 cm. Black knapweed is a dull green plant entirely covered with small, rough hairs. Upright stems are branched at the top, with narrow upper leaves and larger, lobed leaves below. Basal rosette leaves are broad, stalked, and shallowly lobed. Stem leaves are smaller and not lobed. Rose to purple thistle-like flowers at the end of stems, florets being all tubular. Floral bracts have long, black fringes from a dark triangular centre which give the appearance of a black seed head.

Key Identifiers
  • Upper leaves narrow and generally with entire margins, but the lower ones lobed, or with some coarse teeth
  • Whole plant is dull green, rather rough with small hair
  • Woody crown root
  • Dark brown – black bracts; comb-like fringe on margin
  • Stem is swollen below the flowerhead
  • Well visited by nectar insects
Location in Canada
BC, NB, Nfld, NS, Ontario, PEI and Quebec are all know to have this knapweed. Alberta does not have any known reports of black knapweed.

Pacific Northwest Extension Publication - Identification of Knapweed and Starthistles in the Pacific Northwest

Similar species
(Centaurea spp.)Other knapweeds are going to be similar to black knapweed. The key feature for differentiating all knapweeds from one another is to compare the unique bracts. The link under “Resources” is an excellent resource to walk you through identifying knapweeds.
May be mistaken for a thistle at a passing glance but upon inspection, all parts of black knapweed lack spines.

Cindy Roche,

Cindy Roche,


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For more information about the content of this document, contact Chris Neeser.
This document is maintained by Shelley Barkley.
This information published to the web on April 2, 2012.
Last Reviewed/Revised on February 26, 2018.