Spotted Knapweed

Photo Credit: Nicole Kimmel, Alberta Agriculture & Forestry

Common Name: Spotted Knapweed

Scientific Name: Centaurea stoebe

Habitat: roadsides, disturbed areas, gravel pits, grassland, grassland dry

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

Spotted knapweed is native to Eastern Europe. It was introduced to North America as a contaminant in alfalfa seeds in the 1890s.

Legislated Because

Infestations of spotted knapweed form monocultures that displace forage for wildlife and livestock. It prefers to invade disturbed areas in particular. Its roots release chemicals into the soil that inhibit the growth of other plants.

Description

The flowers of spotted knapweed are 6-15 cm wide and the bracts have hair-like margins. These hairs are shorter than the triangular centre of the bract. The bracts also have distinctive dark vertical stripes.

The stem leaves are deeply lobed and each lobe is narrow.

The leaves and the stem are covered in hairs and are grey-green in colour. Each plant has several erect stems that grow 40-150 cm tall.