Squarrose Knapweed

Centaurea virgata L.

Squarrose knapweed
© Weeds of the West

Squarrose knapweed is a native to southwestern Asia and the Middle East.  It is a relatively new invader to North America, being first recorded in California around the 1950’s.  Squarrose knapweed is a long-lived, tap-rooted perennial that usually grows to about 12 inches but may reach 18 inches tall. Its leaves are deeply lobed and, like the stems, are covered with very fine hairs. The flowers are small and pink with bracts that curve outwards. It’s distinguishable from other knapweeds in that diffuse knapweed’s bracts aren’t recurved and spotted knapweed’s bracts have dark spots.  This plant is highly invasive, particularly in native bunch grass and prairie communities.

Squarrose knapweed reproduces mainly by seed dispersal.  Because the plant is a perennial and will re-grow from root reserve for more than 2 years, one plant can produce many seeds over a lifetime.  The morphology of the seeds makes them particularly easy to disperse and they remain viable for many years.

Currently, there has been no infestation in Teton County; however, we know this species has been found elsewhere in Wyoming and neighboring states.  This invader could be very damaging to Teton County if ever introduced.  Due to the threat squarrose knapweed poses to our wildlife habitats, we ask the public to please be on the lookout for this weed species.  www.cdfa.ca.gov

If you find this weed on your property or around Teton County, please report it immediately at 733-8419

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