Fact Sheets


Rhaponticum repens (L.) Hidalgo

Family :

Famille :


Synonym(s) :

Synonyme(s) :

Acroptilon repens (L.) DC

Centaurea repens L.

Centaurea picris Pall. ex Willd.

Common Name(s) :

Nom(s) commun(s) :

Russian knapweed
(English) (GC 2016)

Centaurée de Russie (French) (GC 2016)

Creeping knapweed (English) (CABI 2020)

Hardhead thistle (English) (CABI 2020)

Centaurea rastrera (Spanish) (CABI 2020)

  • Russian knapweed (Rhaponticum repens) achenes

  • Russian knapweed (Rhaponticum repens) achenes

  • Russian knapweed (Rhaponticum repens) achene

  • Russian knapweed (Rhaponticum repens) achene, side view

  • Russian knapweed (Rhaponticum repens) flower head

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Regulation :

Remarques Réglementation:

  • CFIA Weed Seeds Order - Class 2: Primary Noxious Weed Seeds

Regulation Notes:

Distribution :

Répartition :

Native to eastern Europe and temperate Asia and introduced in North America, Argentina, Australia, and beyond its native range in Europe (USDA-ARS 2020). Occurs in Canadian provinces of Alberta, British Columbia, Manitoba, Ontario, and Saskatchewan (Brouillet et al. 2010+).

Habitat and Crop Association :

Habitat et Cultures Associées :

Cultivated fields, old fields, pastures, rangelands, ditches, roadsides, railway lines and disturbed areas (Watson 1980; Darbyshire 2003). Reported as a weed of Medicago sativa (alfalfa) (Watson 1980).

Economic Use, cultivation area, and Weed Association :

Utilisation économique, zone de culture et association de mauvaises herbes :

Duration of Life Cycle :

Durée du cycle vital:


Dispersal Unit Type :

Type d’unité de dispersion :


General Information


Rhaponticum repens was introduced into Canada in the early 1900s as a contaminant in Medicago sativa (alfalfa) seed (Watson 1980). This species is found on a variety of soil types, and has been noted to invade areas where it was not directly introduced (Watson 1980).

R. repens seed can persist in the soil for up to 75 years, and the plants also readily reproduce through stem buds close to the roots (Watson 1980). A dense patch of plants can spread up to 12 square metres in 2 years (Watson 1980). Leaves and stems are also reported to be toxic to horses (Watson 1980).


Rhaponticum repens infestation (Eric Coombs, Oregon Department of Agriculture, Bugwood.org)



  • Achene


    • Achene length*: 2.6 – 4.3 mm; width: 1.2 – 1.9 mm
    *Note: minimum and maximum of 10 achenes in a normal range of this species using  image measurement (ISMA 2020)


    • Egg shaped achene, laterally compressed, with a truncate or rounded wide end, and a notched narrow end

    Surface Texture

    • Achene is smooth with several longitudinal thin ridges


    • Achene is shiny white or greyish yellow coloured, under this thin surface layer is a thicker brown layer
    • Immature achenes are brown coloured

    Other Features


    • Pappus white, narrow, flat bristles, 6.0-11.0 mm long (FNA 1993+), present only on immature achenes

    Achene end with pappus

    • Style remnant at the wide end is a small peg

    Achene end without pappus

    • Small, shallow notch at achene’s narrow end is round or angular shaped
  • Seed


    • Seed similar to achene size


    • Seed is egg shaped

    Surface Texture

    • Seed is smooth


    • Seed is yellowish

    Other Features

    • Seed coat thin, brown, adhering to the fruit wall
  • Embryo


    • Embryo fills the seed


    • Embryo is spatulate, axial position


    • Endosperm is scant, nutritive tissue stored in the cotyledons

    Other Features

    • Cotyledons are oily and soft-textured

Identification Tips


The achenes are distinguished from similar species by their greyish colour, longitudinal ridges, and lack of a pappus. The notch at the narrow end attached to the flower head is small and closer to the end compared to similar Centaurea (knapweed) species with larger notches located on the side of the achene.

Additional Botany Information



  • Flower heads cup shaped, flowers purple or pink, turning straw yellow coloured when mature (CABI 2020).

Vegetative Features

  • Involucral bracts are oblong with thin, translucent tips
  • The area below the tips on inner bracts may have short or curly hairs (CABI 2020)

Similar Species


Similar species are based on a study of seed morphology of various species, and those with similar dispersal units are identified. The study is limited by physical specimen and literature availability at the time of examination, and possibly impacted by the subjectivity of the authors based on their knowledge and experience. Providing similar species information for seed identification is to make users aware of similarities that could possibly result in misidentification.

Grindelia squarrosa (Pursh) Dunal (gumweed)

G. squarrosa achenes are generally narrower (length*: 2.0 – 4.1 mm; width: 0.8 – 1.7 mm), more angular than R. repens, and have a ring of tissue at the base of the achene rather than a notch. G. squarrosa achenes also lack a pappus.

*Note: minimum and maximum of 10 achenes in a normal range of this species using  image measurement (ISMA 2020)

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Brouillet, L., Coursol, F., Meades, S. J., Favreau, M., Anions, M., Bélisle, P. and Desmet, P. 2010+. VASCAN, the database of vascular plants of Canada. http://data.canadensys.net/vascan/ Accessed November 24, 2020.

Centre for Agriculture and Bioscience International (CABI). 2020. Invasive Species Compendium, CAB International, Wallingford, UK. https://www.cabidigitallibrary.org/journal/cabicompendium Accessed November 24, 2020.

Darbyshire, S. J. 2003. Inventory of Canadian Agricultural Weeds. Agriculture and Agri-Food Canada, Research Branch. Ottawa, ON

Flora of North America (FNA) Editorial Committee, eds. 1993+. Flora of North America North of Mexico [Online]. 22+ vols. New York and Oxford.  Accessed December 29, 2022.

Global Biodiversity Information Facility (GBIF) Secretariat. 2022. https://doi.org/10.15468/39omei Accessed via https://www.gbif.org/species/3142208 Accessed December 29, 2022.

Government of Canada (GC). 2016. Canadian Weed Seeds Order. https://laws-lois.justice.gc.ca/eng/regulations/SOR-2016-93/page-2.html (English) https://laws-lois.justice.gc.ca/fra/reglements/DORS-2016-93/page-2.html (French)

International Seed Morphology Association (ISMA). 2020. Method for Seed Size Measurement. Version 1.0. ISMA Publication Guide.

U.S. Department of Agriculture-Agricultural Research Services (USDA-ARS). 2020. Germplasm Resources Information Network (GRIN), https://npgsweb.ars-grin.gov/gringlobal/taxon/taxonomysimple.aspx Accessed November 24, 2020.

Watson, A. K. 1980. The Biology of Canadian Weeds 43. Acroptilon (Centaurea repens (L.) DC. Canadian Journal of Plant Science, 1980, 60 (3): 993-1004.



Jennifer Neudorf, Angela Salzl, Ruojing Wang, Karen Castro, Katrina Entwistle

Canadian Food Inspection Agency