Centaurea virgata var. squarrosa

Centaurea virgata var. squarrosa_squarrose knapweed_JM DiTomaso_cropped
Photo: 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?

CDFA Rating: -*?


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 - Distribution map and records of this species in California.
  • CalWeedMapper - Distribution map of this species in California with ability to determine regional priorities.
  • EDDMapS - Distribution of this species in North America.
  • Jepson Interchange - Information on this plant's taxonomy, biology, and distribution from UC Berkeley's Jepson Herbarium.
  • USDA PLANTS Database - Information on identification and distribution, with links to websites in individual states.
  • Additional photos

    Centaurea virgata ssp. squarrosa_flower heads_ZoyaAkulova
    Centaurea virgata ssp. squarrosa (squarrose knapweed) flower heads. Photo: Zoya Akulova
    Centaurea virgata ssp. squarrosa_rosette_ZoyaAkulova
    Centaurea virgata ssp. squarrosa (squarrose knapweed) rosette. Photo: Zoya Akulova
    Centaurea virgata ssp. squarrosa_seeds_copyright_DeanKelch(CDFA)
    Centaurea virgata ssp. squarrosa (squarrose knapweed) seeds. Photo: &#169 Dean Kelch, CDFA
    Centaurea virgata ssp. squarrosa_growth habit_copyright_DeanKelch(CDFA)
    Centaurea virgata ssp. squarrosa (squarrose knapweed) growth habit. Photo: &#169 Dean Kelch, CDFA