Acroptilon repens - (L.) DC.
Russian Knapweed
Other English Common Names: Hardheads, Turkestan Thistle
Other Common Names: hardheads
Synonym(s): Centaurea repens L. ;Rhaponticum repens (Linnaeus) Hidalgo
Taxonomic Status: Accepted
French Common Names: centaurée de Russie
Unique Identifier: ELEMENT_GLOBAL.2.133746
Element Code: PDASTD2010
Informal Taxonomy: Plants, Vascular - Flowering Plants - Aster Family
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Asterales Asteraceae Acroptilon
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Concept Reference
Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Acroptilon repens
Taxonomic Comments: Susanna and Garcia-Jacas (2007) transfer Acroptilon repens to Rhaponticum repens.
Conservation Status

NatureServe Status

Global Status: GNR
Global Status Last Changed: 22Mar1994
Rounded Global Status: GNR - Not Yet Ranked
Nation: United States
National Status: NNA
Nation: Canada
National Status: NNA (18Nov2017)

U.S. & Canada State/Province Status
Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
United States Arizona (SNA), Arkansas (SNA), California (SNA), Colorado (SNA), Idaho (SNA), Illinois (SNA), Indiana (SNA), Iowa (SNA), Kansas (SNA), Kentucky (SNA), Michigan (SNA), Missouri (SNA), Montana (SNA), Nebraska (SNA), Nevada (SNA), New Mexico (SNA), North Dakota (SNA), Ohio (SNA), Oklahoma (SNA), Oregon (SNA), South Dakota (SNA), Texas (SNA), Utah (SNA), Virginia (SNA), Washington (SNA), Wisconsin (SNA), Wyoming (SNA)
Canada Alberta (SNA), British Columbia (SNA), Manitoba (SNA), Ontario (SNA), Saskatchewan (SNA)

Other Statuses

NatureServe Global Conservation Status Factors

Other NatureServe Conservation Status Information

U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States ARexotic, AZexotic, CAexotic, COexotic, IAexotic, IDexotic, ILexotic, INexotic, KSexotic, KYexotic, MIexotic, MOexotic, MTexotic, NDexotic, NEexotic, NMexotic, NVexotic, OHexotic, OKexotic, ORexotic, SDexotic, TXexotic, UTexotic, VAexotic, WAexotic, WIexotic, WYexotic
Canada ABexotic, BCexotic, MBexotic, ONexotic, SKexotic

Range Map
No map available.

Ecology & Life History Not yet assessed
Economic Attributes Not yet assessed
Management Summary Not yet assessed
Population/Occurrence Delineation Not yet assessed
Population/Occurrence Viability
U.S. Invasive Species Impact Rank (I-Rank)
Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: High/Medium
Rounded I-Rank: High
I-Rank Reasons Summary: Mostly recognized as a weed of cultivated fields, orchards and pastures, Acroptilon repens also invades nearby natural areas. A strong competitor, it forms dense monocultures that exclude other vegetation. Originally introduced in the early 1900s, it has spread across the U.S. and is now found in most states.
Subrank I - Ecological Impact: Medium/Low
Subrank II - Current Distribution/Abundance: High
Subrank III - Trend in Distribution/Abundance: High/Medium
Subrank IV - Management Difficulty: High/Medium
I-Rank Review Date: 01Jul2004
Evaluator: Fellows, M.
Native anywhere in the U.S?
Native Range: Native to temperate Asia from eastern Europe to Mongolia, south into Iran and Iraq (GRIN 2001).

Download "An Invasive Species Assessment Protocol: Evaluating Non-Native Plants for their Impact on Biodiversity". (PDF, 1.03MB)
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Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: (Kartesz 1999).

S-2. Present in conservation areas or other native species habitat? Yes
Comments: (Carpenter and Murray)

Subrank I - Ecological Impact: Medium/Low

1. Impact on Ecosystem Processes and System-wide Parameters:Medium significance/Insignificant
Comments: Inferred from lack of reports in the literature of significant ecosystem damage.

2. Impact on Ecological Community Structure:Medium/Low significance
Comments: Perennial forb (Kartesz 1999) that forms dense colonies (Whitson et al. 1996).

3. Impact on Ecological Community Composition:High significance
Comments: Can form dense, monospecific colonies that exclude native plants through physical and allelopathic mechanisms (Carpenter and Murray). Allelopathic chemicals can stay in the soil after Acroptilon repens has been removed.

4. Impact on Individual Native Plant or Animal Species:Low significance
Comments: Grassland and shrubland species are excluded as a result of Acroptilon repens presence, including: Festuca scabrella, Festuca idahoensis, Agropyron spicatum, Stipa occidentalis, and Stipa richardsonii (Carpenter and Murray).

5. Conservation Significance of the Communities and Native Species Threatened:Low significance/Insignificant
Comments: Most commonly invades waste places and cultivated fields, but also found in meadows, grasslands and riparian areas (Carpenter and Murray).

Subrank II. Current Distribution and Abundance: High

6. Current Range Size in Nation:High significance
Comments: Found throughout western US and the mid-west (Kartesz 1999).

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:High significance
Comments: Considered a state-level noxious weed in nearly every state west of the Mississippi River (Kartesz 1999).

8. Proportion of Nation's Biogeographic Units Invaded:High significance
Comments: Potentially occurs in over 75% of TNC ecoregions (inferred from Kartesz 1999 and TNC 2001).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:Low significance
Comments: Found in a variety of cultivated situations (fields, orchards, pastures) and roadsides (Whitson 1996). Also in meadows, waste places and irrigation ditches (Agricultre Research Service 1970) and riparian areas (Carpenter and Murray).

Subrank III. Trend in Distribution and Abundance: High/Medium

10. Current Trend in Total Range within Nation:High/Moderate significance
Comments: In 1955 it was reported to be spreading into Texas, and Michigan (Muenscher 1955). By 1970 it had reached TX and MI (Agriculture Research Service 1970). Given the current distribution (Kartesz 1999), it has clearly spread beyond that range.

11. Proportion of Potential Range Currently Occupied:Unknown

12. Long-distance Dispersal Potential within Nation:High significance
Comments: Spreads primarily by roots (may be 7 meters long) and seeds (Carpenter and Murray). Also spread on contaminated farm equipment.

13. Local Range Expansion or Change in Abundance:High/Moderate significance
Comments: Spreads rapidly; a single plant can cover a 12 meter squared area in 2 years (Carpenter and Murray).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:Low significance
Comments: Preferred habitats are associated with frequent disturbance (Whitson 1996). In addition, it does not establish readily in healthy, natural habitats (Carpenter and Murray).

15. Similar Habitats Invaded Elsewhere:High/Low significance
Comments: Present in Canada (Kartesz 1999).

16. Reproductive Characteristics:Moderate significance
Comments: Spreads from roots (Whitson 1996) and seeds (Muenscher 1955). Even though it reproduces primarily through vegetative means, it can produce 1200 seeds/year/plant (Carpenter and Murray). Seeds may remain viable between 2 and 8 years (Carpenter and Murray).

Subrank IV. General Management Difficulty: High/Medium

17. General Management Difficulty:High significance
Comments: In 2000, USDA was attempting to test biocontrol agents for Acroptilon repens (Morse, pers. comm. 2000). In fields, till and plant a smother crop (Muenscher 1955), which suggests planting a native canopy might reduce infestations (Carpenter and Murray). Difficult to control or eradicate once established (CWMA 1999).

18. Minimum Time Commitment:High/Moderate significance
Comments: No single method obtains complete control in a short time period; usually requires "aggressive" monitoring and control over several years (Carpenter and Murray). After initial control, follow up management is required to maintain area weed free (Carpenter and Murray). Native plants may be slow to return due to the continuing presence of allelopathic compunds in soil (Carpenter and Murray). The extensive root system allows stands to survive decades (Carpenter and Murray).

19. Impacts of Management on Native Species:Unknown

20. Accessibility of Invaded Areas:Unknown

Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

  • Watson, A. K. 1980. The biology of Canadian weeds. 43. Acroptilon (Centaurea) repens. Canadian Journal of Plant Science 60: 993-1004.

  • Agricultural Research Service. 1970. Common weeds of the United States. Agricultural Research Service, U.S. Department of Agriculture. Washington, D.C. 463 pp.

  • Carpenter, Alan T. and Thomas A. Murray. No Date. Element Stewardship Abstract for Acroptilon repens (L.) De Candolle (Centaurea repens (L.)) Russian knapweed. Land Stewardship Consulting, Boulder, CO. Prepared for The Nature Conservancy, Arlington, VA. (accessed 2004).

  • Colorado Weed Management Association (CWMA). 1999. Noxious weeds and non-native plant factsheets. Available: (Accessed 2002).

  • Dorn, R. D. 2001. Vascular Plants of Wyoming, third edition. Mountain West Publishing, Cheyenne, WY.

  • Douglas, G.W., G.D. Straley, and D. Meidinger, eds. 1998b. Illustrated Flora of British Columbia, Vol. 1, Gymnosperms and Dicotyledons (Aceraceae through Asteraceae). B.C. Minist. Environ., Lands and Parks, Wildl. Branch, and B.C. Minist. For. Res. Program. 436pp.

  • Flora of North America Editorial Committee. 2006a. Flora of North America North of Mexico. Vol. 19. Magnoliophyta: Asteridae, part 6: Asteraceae, part 1. Oxford University Press, New York. xxiv + 579 pp.

  • Hidalgo, O., N. Garcia-Jacas, T. Garnatje, and A. Susanna. 2006. Phylogeny of Rhaponticum (Asteraceae, Cardueae?Centaureinae) and Related Genera Inferred from Nuclear and Chloroplast DNA Sequence Data: Taxonomic and Biogeographic Implications. Annals of Botany 97: 705?714.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1996. Species distribution data at state and province level for vascular plant taxa of the United States, Canada, and Greenland (accepted records), from unpublished data files at the North Carolina Botanical Garden, December, 1996.

  • Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.

  • Kartesz, J.T., and R. Kartesz. 1980. A synonymized checklist of the vascular flora of the United States, Canada and Greenland. Vol. 2. The biota of North America. Univ. of North Carolina Press, Chapel Hill. 500 pp.

  • Muenscher, W. C. 1955. Weeds. The MacMillan Co., New York.

  • Scoggan, H.J. 1957. Flora of Manitoba. National Museum of Canada, Bulletin number 140.

  • Scoggan, H.J. 1978. The Flora of Canada. National Museum of Natural Sciences, National Museum of Canada, Publ. in Botany 7(4).

  • Susanna, A. and N. Garcia-Jacas. 2007. Tribe Cardueae Cass. (1819). pp. 123-147 in J.W. Kadereit and C. Jeffrey (eds.), The Families and Genera of Vascular Plants (K. Kubitzki, ser. ed.), VIII. Flowering Plants - Eudicots. Asterales, Springer Verlag, Berlin.

  • The Nature Conservancy. 2001. Map: TNC Ecoregions of the United States. Modification of Bailey Ecoregions. Online . Accessed May 2003.

  • USDA, ARS, National Genetic Resources Program. 2001. Germplasm Resources Information Network - (GRIN). [Online Database]. National Germplasm Resources Laboratory, Beltsville, Maryland.URL: (Accessed 2004)

  • Voss, E. G., and A. A. Reznicek. 2012. Field Manual of Michigan Flora. University of Michigan Press, Ann Arbor. 990 pp.

  • Weber, W. A. and R. C. Wittmann. 1992. Catalog of The Colorado Flora: A Biodiversity Baseline. University Press of Colorado, Niwot, CO.

  • Whitson, T.D. (ed.), L.C. Burrill, S.A. Dewey, D.W. Cudney, B.E. Nelson, R.D. Lee, R. Parker. 1996. Weeds of the West. 5th edition. The Western Society of Weed Science in cooperation with the Western United States Land Grant Universities Cooperative Extension Services, Newark, CA. 630 pp.

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