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Squarrose Knapweed

Photo Credit: Steve Dewey, Utah State University, retrieved from Bugwood.org (Image Number: 1459278), used under CC BY 3.0 US, modified from the original

Common Name: Squarrose Knapweed

Scientific Name: Centaurea virgata

Habitat: roadsides, grassland, grassland dry, grassland wet

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

Squarrose knapweed is native to southwest Asia and the Middle East. The method of its introduction into North America is unknown. During the 1950s it became a problematic species on rangeland in the western U.S.

Legislated Because

Squarrose knapweed is well adapted to drought and to cold temperatures. It can invade rangeland and out-compete forage species causing a negative impact on livestock and wildlife.

Description

This knapweed has very small flowers that are only 3-8 mm wide. The bracts have a distinctive short spine that curves backwards at the tip.

The leaves are deeply lobed, grey-green in colour and have hairs on the surface. They get progressively smaller from the base to the top of the stem. The fruits usually don't have a plume or bristles.

Squarrose knapweed grows up to 150 cm tall.