Diffuse Knapweed (Centaurea diffusa)

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A winter-hardy biennial or short-lived perennial with a taproot. The single upright stem grows 15 to 60 cm in height and has numerous branches mostly on the upper half. The deeply lobed basal leaves are up to 10 cm long and 2.5 cm wide and arranged in a low-lying rosette. Lower stem leaves are alternate and divided into many lobes, whereas upper stem leaves are much smaller and have only a few slender lobes. Flowers are predominantly white, occasionally pink-purple. Heads are 1.3 cm long and covered with small, narrow bracts ending in sharp, rigid spines. The terminal spine is distinctly longer than the lateral, spreading spines. Specialized chemicals give this weed a distinctive smell and an extremely bitter taste.

Key Identifiers
  • Stems are upright, highly branched, and angled, with short, stiff hairs on the angles
  • Flowers solitary or in clusters of 2-3 at the ends of the branches
  • Heads contain two types of flowers, ray flowers around the edges surrounding tubular disk flowers
  • Unlike other knapweeds, the heads of diffuse do not open to shed seeds
Location in Canada
BC, Ontario, Quebec, SK, Yukon and Alberta are all known to have populations of diffuse knapweed.

Resources Similar species
(Centaurea spp.) Other knapweeds are going to be similar to diffuse knapweed. The key feature for differentiating all knapweeds from one another is to compare the unique bracts. The first link under “Resources” is an excellent resource to walk you through identifying knapweeds.

Other Documents in the Series

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Diffuse Knapweed (Centaurea diffusa) - Current Document
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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 August 21, 2018.