Centaurea virgata var. squarrosa

Photo courtesy Joseph DiTomaso

Synonyms: Centaurea squarrosa Willd. is an illegally applied name according to the rules of the International Code of Botanical Nomenclature (Saint Louis Code) since the name Centaurea squarrosa Roth was previously applied to a different species. Centaurea virgata Lam. var. squarrosa (Willd.) Boiss. is a synonym of Centaurea squarrosa Willd. Some taxonomists are using the name C. triumfetti All. for diffuse knapweed. Some flora use C. virgata Lam. ssp. squarrosa (Willd.) Gugler, but the taxon was given variety ranking first.

Common names: squarrose knapweed

Centaurea virgata var. squarrosa (squarrose knapweed) is a perennial (family Asteraceae) found in the Klamath and Cascade Ranges, Modoc Plateau and northern Sierra Nevada Mountains of California. Squarrose knapweed favors disturbed open sites, including degraded rangeland, logged areas, grasslands and roadsides. Squarrose knapweed seed dispersal is enhanced by soil and water movement, and by clinging to humans and animals. Seed dispersal and reproduction can be limited by mowing or mechanical removal of plants before seed-set. Squarrose knapweed is a listed noxious weed in several western states.

Cal-IPC Rating: Moderate

Cal-IPC Assessment

Plant Assessment Form - Information gathered by Cal-IPC on the impacts, rate of spread, and distribution of invasive plants in California. Does not include management information.

Weed Management Notes

  • Management Notes - Information on management techniques and effectiveness from the University of California Cooperative Extension’s Weed Research & Information Center.

Cal-IPC Newsletter Articles

Cal-IPC Symposium Presentations

Presentations are linked where available. Where a presentation is not available, find more information by reading the abstract in the Cal-IPC Symposia Archive.

There are no Symposium presentations associated with this species yet.

Other Centaurea virgata var. squarrosa Information

  • CalPhotos - Images of plants taken mostly in California.
  • Calflora - See the distribution of this species on Calflora's map of California.
  • CalWeedMapper - Distribution information with ability to determine regional priorities.
  • Jepson Online Interchange for California Flora - Information on taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • CDFA - California official noxious weeds.
  • USDA PLANTS Database - Federal database with information on identification and distribution, and links to websites in individual states.