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Diffuse Knapweed

Diffuse knapweed
Photo Credit: Nicole Kimmel, Alberta Agriculture & Forestry

Common Name: Diffuse knapweed

Scientific Name: Centaurea diffusa

Habitat: roadsides, disturbed areas, farmland, grassland

Provincial Designation: Prohibited Noxious

Prohibited Noxious weeds are plant species that are designated as "prohibited noxious" in the Alberta weed regulation. Prohibited noxious weeds must be destroyed, meaning all growing parts need to be killed or the plant's reproductive mechanisms need to be rendered non-viable.

Origin

Diffuse knapweed is native to Eurasia and was introduced to North America in the late 1800s as a contaminant in alfalfa and clover seed.

Legislated Because

Diffuse knapweed becomes tough and unpalatable late in the season which causes grazing animals to avoid using this plant as forage. It can quickly establish on disturbed sites and invade native plant communities. Once established, it can form large infestations in both rural and urban areas.

Description

The flowers of diffuse knapweed are white to pink in colour and are surrounded by triangular bracts that narrow into short, stiff spines. Leaves are alternate, deeply lobed, and covered in fine hairs that give them a grey-green appearance.

Diffuse knapweed has a single upright stem that can reach heights up to 100 cm.

It commonly causes rashes when touched with bare skin.