California Invasive Plant Council

Centaurea stoebe ssp. australis

Synonyms: Centaurea stoebe ssp. micranthus; Centaurea maculosa; Centaurea biebersteinii

Common names: spotted knapweed

Centaurea stoebe subsp. australis (spotted knapweed) is a  biennial or perennial forb (family Asteraceae). A native of Europe and western Asia, it was accidentally introduced into North America in the late 1800s in contaminated alfalfa and clover seed and in soil used for ship ballast. Rosettes and cauline leaves are grey-green and deeply lobed and single-seeded fruits (achenes) have a pappus of uneven bristles. Plants favors disturbed open sites, grasslands, overgrazed rangelands, roadsides and logged areas. Spotted knapweed crowds out native species and forage for livestock, and can invade undisturbed native bunchgrass stands. An individual plant may produce as many as 40,000 seeds. Plants in California are assumed to be the tetraploid “australis” subspecies.

Cal-IPC Rating: High?

Explanation of Cal-IPC ratings

• High – These species have severe ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal and establishment. Most are widely distributed ecologically.
• Moderate – These species have substantial and apparent-but generally not severe-ecological impacts on physical processes, plant and animal communities, and vegetation structure. Their reproductive biology and other attributes are conducive to moderate to high rates of dispersal, though establishment is generally dependent upon ecological disturbance. Ecological amplitude and distribution may range from limited to widespread.
• Limited – These species are invasive but their ecological impacts are minor on a statewide level or there was not enough information to justify a higher score. Their reproductive biology and other attributes result in low to moderate rates of invasiveness. Ecological amplitude and distribution are generally limited, but these species may be locally persistent and problematic.
• Alert – An Alert is listed on species with High or Moderate impacts that have limited distribution in California, but may have the potential to spread much further.
• Watch – These species have been assessed as posing a high risk of becoming invasive in the future in California.

CDFA Rating: -*?

Explanation of CDFA ratings

• A – A pest of known economic or environmental detriment and is either not known to be established in California or it is present in a limited distribution that allows for the possibility of eradication or successful containment.
• B – A pest of known economic or environmental detriment and, if present in California, it is of limited distribution.
• C – A pest of known economic or environmental detriment and, if present in California, it is usually widespread.
• D – An organism known to be of little or no economic or environmental detriment, to have an extremely low likelihood of weediness, or is known to be a parasite or predator.
• Q – An organism or disorder suspected to be of economic or environmental detriment, but whose status is uncertain because of incomplete identification or inadequate information.
• * – An asterisk next to the rating indicates that a plant is included in the CCR Section 4500 list of California State Noxious Weeds.
• -* – This plant is included in the CCR Section 4500 list of California State Noxious Weeds, but is otherwise not rated.

More details

Assessment(s)

Centaurea stoebe ssp. australis 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.

Species ID Card

Invasive Species ID Card - To support field identification of early detection species, Cal-IPC has designed a set of Species ID cards that can be downloaded, printed double-sided, and trimmed to size.

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

• Weed biological control agents approved for California. Pitcairn, Michael J.; Smith, Lincoln; Moran, Patrick. Vol 22, Issue 1
• Jepson Manual 2nd ed. invasive plant name changes. Brusati, Elizabeth. Vol 20, Issue 2
• Prioritizing Regional Response to Invasive Plants in the Sierra Nevada. Brusati, Elizabeth; Morawitz, Dana; Powell, Cynthia. Vol 19, Issue 2
• Wildland Weed News. editor. Vol 17, Issue 2
• Tackling invasive plants on California Sept. of Fish & Game lands. O'Rourke, Brianne; Horenstein, Julie. Vol 17, Issue 1
• Fighting weeds in the Tahoe basin. Donaldson, Sue. Vol 11, Issue 2

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.

• Regional EDRR with Bay Area WMAs. Johnson, Doug; Valentine, Nicole (2022)
• Weeds and seeds and fire, oh my! Weed management lessons from Montana. Mangold, Jane (2022)
• Floodplains restoration post-infestation on the North Fork Salmon River. Malone-Persha, Deja (2020)
• Using detection dogs to enhance invasive plant management strategies. Hurt, Aimee (2020)
• 2002 Red alert! New introductions and recent expansions in California. Tu, Mandy; Randall, John M. (2002)

Other Centaurea stoebe ssp. australis Information

• CalPhotos - Images of plants taken mostly in California.
• Calflora - Distribution map and records of this species in California.
• 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