Fact Sheets


Centaurea iberica Trevir. ex Spreng.

Family :

Famille :


Synonym(s) :

Synonyme(s) :

Calcitrapa iberica (Spreng.) Schur (POWO 2020)

Common Name(s) :

Nom(s) commun(s) :

Iberian starthistle
(English) (GC 2016)

Iberian knapweed (English) (ITIS 2020)

  • Iberian starthistle (Centaurea iberica) achenes

  • Iberian starthistle (Centaurea iberica) achene, side view

  • Iberian starthistle (Centaurea iberica) achene, top-down view

  • Iberian starthistle (Centaurea iberica) achene, basal notch

Explore More :

Explore plus :



Regulation :

Remarques Réglementation:

  • CFIA Weed Seeds Order - Class 1: Prohibited Noxious Weed Seeds
  • List of Pests Regulated by Canada

Regulation Notes:

Prohibited Noxious, Class 1 in the Canadian Weed Seeds Order (2016) under the Seeds Act. All imported and domestic seed must be free of Prohibited Noxious weed seeds.

Distribution :

Répartition :

Native to Asia and Europe (USDA-ARS 2020). Introduced in the United States (California, Kansas, Oregon, Washington, Wyoming) (CABI 2020; USDA-ARS 2020). Also introduced in Argentina and outside of its native range in Europe (CABI 2020; USDA-ARS 2020). Absent from Canada (Brouillet et al. 2010+).

Habitat and Crop Association :

Habitat et Cultures Associées :

Fields, pastures, rangelands, woodlands, shrub lands, banks of watercourses, roadsides and disturbed areas (DiTomaso and Healy 2007; CABI 2020). In the United States, it is highly competitive along roadsides and in rangelands (ODA Undated).

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:

Biennial, annual or perennial

Dispersal Unit Type :

Type d’unité de dispersion :


General Information


Centaurea iberica was accidently introduced into the western United States, from where it has since spread, most notably in the 1920s (DiTomaso and Healy 2007) and the 1950s (Graham and Johnson 2003).




  • Achene


    • Achene length*: 3.2 – 4.0 mm; width: 1.3 – 2.1 mm
    *Note: minimum and maximum of 10 achenes in a normal range of this species using  image measurement (ISMA 2020)


    • Oblong shaped achene with a narrow rounded notched end and a wider truncate end, laterally compressed

    Surface Texture

    • Achene is smooth


    • Achene is generally shiny white with brown streaks, but can be solid white coloured

    Other Features


    • Pappus length: 1.0 – 2.5 mm (FNA 1993+)
    • White pappus is composed of flat bristles of variable lengths in several rings. Outer pappus bristles are the shortest, increasing in length towards the inside, the innermost bristles cover the style remnant

    Achene end with pappus

    • A small style remnant is present in the center of the truncate end

    Achene end without pappus

    • The notch at the narrow end is generally shallow but long relative to the achene size, making the rounded end look narrow
    • The surface is glossy light yellow-coloured around side notch
  • Seed


    • Seed size similar to achene size


    • Seed is oblong shaped

    Surface Texture

    • Seed surface is smooth


    • Seed is orange or yellow coloured

    Other Features

    • Seed coat brown, adhering to fruit wall
  • Embryo


    • The embryo fills the seed


    • Embryo is spatulate, axial position


    • Endosperm absent, nutritive tissue stored in the cotyledons

    Other Features

    • Cotyledons are fleshy and soft-textured

Identification Tips


The combination of a shining brown streaked pattern is distinctive, along with a light yellow side notch and persistent pappus.

Additional Botany Information



  • Flower heads oval shaped, flowers white, pink or purple (FNA 1993+)

Vegetative Features

  • Involucral bracts are broad oval shaped, tipped with a long, straw yellow spine and smaller spines near the base

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.

Centaurea calcitrapa L. (purple starthistle)

The achenes of C. calcitrapa are generally smaller (length*: 2.4 – 3.0 mm), have a smaller side notch, generally dull reddish-brown streaked pattern and lack a pappus compared to C. iberica.

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

Click to select species

Cliquez pour sélectionner les espèces

Comparison Window

Fenêtre de comparaison

Need ID Help?

Besoin d’aide pour l’identification?



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 October 15, 2020.

Centre for Agriculture and Bioscience International (CABI). 2020. Invasive Species Compendium, CAB International, Wallingford UK. https://www.cabidigitallibrary.org/journal/cabicompendium Accessed October 8, 2020.

DiTomaso, J. M. and Healy, E. A. 2007. Weeds of California and Other Western States. Vol. 1. 834 pp. University of California, CA.

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

Global Biodiversity Information Facility (GBIF) Secretariat. 2022. https://doi.org/10.15468/39omei Accessed via https://www.gbif.org/species/3129000 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)

Graham, J. and Johnson, W. S. 2003. Managing Purple and Iberian Starthistles, www.unce.unr.edu/publications/files/nr/2003/FS0346.pdf Accessed May 30, 2016.

Integrated Taxonomic Information System (ITIS). 2020. https://www.itis.gov/ Accessed June30, 2020.

International Seed Morphology Association (ISMA). 2020. Method for Seed Size Measurement. Version 1.0. ISMA Publication Guide.   https://www.idseed.org/authors/details/method_for_seed_size_measurement.html

Oregon Department of Agriculture (ODA). 2020. Oregon Noxious Weed Profiles. Iberian starthistle Centaurea iberica, https://www.oregon.gov/oda/shared/Documents/Publications/Weeds/IberianStarthistleProfile.pdf Accessed October 8, 2020.

Plants of the World Online (POWO). 2020. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; http://www.plantsoftheworldonline.org/ Accessed October 8, 2020.

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 October 15, 2020.



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

Canadian Food Inspection Agency