California Invasive Plant Council

Rhaponticum repens

Synonyms: Acroptilon repens, Centaurea repens

Common names: Russian knapweed, hardheads, creeping knapweed, mountain bluet, Turkestan thistle

Rhaponticum repens (Russian knapweed) is an aggressive perennial forb (family Asteraceae) that is native to Eurasia and has been expanding in California. It is now found across the state. Rosettes are gray-green and deeply pinnately lobed. Upper cauline leaves are small, sessile, and not lobed. Flowers are pink to lavender and flower heads contain only tubular (disk) florets; flower heads are smooth, globular, with whitish-edged bracts. Plant are deep-rooted and long-lived. This plant crowds out native species and is toxic to horses. Russian knapweed is of particular concern in more disturbed habitats, such as rangeland and agricultural land. It may have allelopathic properties.

Cal-IPC Rating: Moderate?

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: B*?

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)

Rhaponticum repens 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

• Prioritizing Regional Response to Invasive Plants in the Sierra Nevada. Brusati, Elizabeth; Morawitz, Dana; Powell, Cynthia. Vol 19, Issue 2
• 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.

• Biological control agents of weeds in California: Overview of rearing, releases, and monitoring by the CDFA Biological Control Program. Moran, Patrick (2023)
• Preventing weed spread via contaminated hay and straw. Clines, Joanna (2005)
• Getting the job done: Working within the regulatory environment at Lake Tahoe to manage weeds. Donaldson, Susan; West, Wendy; Taylor, Kirk (2003)
• How the west was lost: Reconstructing the invasion dynamics of yellow star-thistle and other plant invaders of western rangelands and natural areas. Gerlach, John D. (1997)

Other Rhaponticum repens Information

• Bugwood - National database from the Center for Invasive Species and Ecosystem Health at the University of Georgia.
• 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