Invasive Species Council of British Columbia
Invasive Plant

Diffuse knapweed

Centaurea diffusa

About This Species

Diffuse knapweed (White knapweed, Tumble knapweed) is often found growing in open areas and well-drained soils where they establish in grasslands, open forests, and along roadsides – it is uncommon on cultivated land. It was likely unintentionally introduced to North America from Eastern Europe and the Mediterranean. They choke out desirable forage for livestock and wildlife and increase soil erosion. These plants can produce up to 18,000 seeds per year that can remain dormant in the soil for a long time. Seeds can be spread by wind, livestock, and people. Diffuse knapweed is designated as a Provincial Noxious Weed by the BC Weed Control Act. 

How to Identify

Diffuse knapweed grows to 0.1-0.6 m as a slender, short flowering plant. 

The flowers are white or sometimes purple, found in clusters or solitary at the end of branches with small, sharp, rigid spines on the bracts. Bracts are yellowish with a brownish margin, sometimes spotted, fringed on the sides, and terminating in a slender bristle or spine. Seeds are light brown to black in colour. 

Its leaves are hairy, greyish-green, and split on many branches growing from a single upright stem. It has larger, hairy leaves at the base of the plant that get smaller as they go up the stem. 

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Diffuse knapweed is a PlantWise "Alert" species - Gardeners should avoid purchasing or planting.


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