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Weed Seed: Centaurea diffusa (Diffuse knapweed)



Common name

Diffuse knapweed


Prohibited Noxious, Class 1 in the Canadian Weed Seeds Order, 2016 under the Seeds Act. All imported and domestic seed must be free of Prohibited Noxious weed seeds.


Canadian: Occurs in AB, BC, ON, QC, SK (Brouillet et al. 2016Footnote 1).

Worldwide: Native to southeastern Europe and western Asia and it has expanded beyond its native range into central and western Europe and has also been introduced into North America and Argentina (CABI 2016Footnote 2).

Duration of life cycle

Biennial or short-lived perennial

Seed or fruit type


Identification features



Surface texture


Habitat and crop association

Fields, rangelands, grasslands, dunes, open forests, roadsides, railway lines, gravel pits, industrial sites and other disturbed areas (Darbyshire 2003Footnote 3, CABI 2016Footnote 2). A serious weed of alfalfa in its native range but mainly a weed of rangelands (CABI 2016Footnote 2).

General information

Diffuse knapweed can be found over a wide range of soil and environmental conditions but cannot tolerate cultivation or excessive moisture (CABI 2016Footnote 2). Diffuse knapweed produces large numbers of seeds that are dispersed by wind, water, and animals. Plant stems may break off to become tumbleweeds, dispersing seeds over large distances (CABI 2016Footnote 2).

Similar species

Spotted knapweed (Centurea stoebe)


Diffuse knapweed (Centurea diffusa) achenes
Diffuse knapweed (Centurea diffusa) achene
Diffuse knapweed (Centurea diffusa) achene, basal notch
Diffuse knapweed (Centurea diffusa) flower head
Diffuse knapweed (Centurea diffusa) achenes

Similar species

Similar species: Spotted knapweed (Centurea stoebe) achenes
Similar species: Spotted knapweed (Centurea stoebe) achene
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