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Centaurea stoebe L.

Overview
General Information
ID Info
Similar Species
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Aperçu
Renseignements Généraux
Informations D'identification
Espèces Semblables
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Family :

Famille :

Asteraceae

Synonym(s) :

Synonyme(s) :

Centaurea maculosa Lam.

Common Name(s) :

Nom(s) commun(s) :

Spotted knapweed
(English) (GC 2016)

Centaurée maculée (French) (GC 2016)

Spotted knapweed (Centaurea stoebe) achenes

  • Spotted knapweed (Centaurea stoebe) achenes

  • Spotted knapweed (Centaurea stoebe) achenes

  • Spotted knapweed (Centaurea stoebe) achene

  • Spotted knapweed (Centaurea stoebe) achene; basal notch

  • Spotted knapweed (Centaurea stoebe) achene, top-down view

  • Spotted knapweed (Centaurea stoebe) achene, close-up

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Overview

Aperçu

Regulation :

Remarques Réglementation:

  • CFIA Weed Seeds Order - Class 1: Prohibited Noxious Weed Seeds
  • Quarantine lists of countries e.g. India *may be updated without notice

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 parts of Europe and widely naturalized in others (USDA-ARS 2020). Introduced in Canada and the United States and Australia and New Zealand (CABI 2020; USDA-ARS 2020). Occurs in Canadian provinces of Alberta, British Columbia, New Brunswick, Nova Scotia, Ontario, Quebec, Saskatchewan, Yukon (Brouillet et al. 2010+).

Habitat and Crop Association :

Habitat et Cultures Associées :

Rangelands, grasslands, roadsides, riverbanks and disturbed areas (CABI 2020). Reported as a weed of Medicago sativa (alfalfa) but not usually associated with crop production (CABI 2020).

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:

Perennial

Dispersal Unit Type :

Type d’unité de dispersion :

Achene

General Information

RENSEIGNEMENTS GÉNÉRAUX

Centaurea stoebe was accidentally introduced to North America in contaminated Medicago sativa (alfalfa) and Trifolium spp. (clover) seed in the late 1800s (Ochsmann 2001).

C. stoebe can thrive over a wide range of climate and soil conditions although it prefers well-drained, light to coarse textured soils (CABI 2020). Achenes are dispersed close to the plant, and may be carried a short distance attached to animals, or longer distances by water or vehicle activity (Watson and Renney 1974; Sheley et al. 1998).

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Centaurea stoebe infestation (Leslie J. Mehrhoff, University of Connecticut, Bugwood.org)

Identification

Identification

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  • Achene

    Size

    • Achene length*: 1.8 – 3.1 mm; width: 0.8 – 1.3 mm
    *Note: minimum and maximum of 20 achenes in a normal range of this species using image measurement (ISMA 2020)

    Shape

    • Achene oblong shaped with a narrow, notched end and a wider truncate end with a pappus, laterally compressed

    Surface Texture

    • Achene surface is smooth, can have scattered surface hairs that are generally removed during processing

    Colour

    • Achene colour varies from dull or shining light yellow, light brown, brown or dark greenish-brown with a wide, light yellow central stripe, may have additional thin stripes to either side

    Other Features

    Pappus

    • Pappus length: up to 5.0 mm (FNA 1993+)

    Achene end with pappus

    • A small style remnant is present in the center of the truncate end
    • The rim around the truncate end may be lighter than or the same as the achene’s dominant colour

    Achene end without pappus

    • The side notch at the end attached to the flower head is deeper and longer compared to similar Centaurea species.
    • The area around the side notch is generally shiny or glossy light yellow
    • Tissue (elaiosome) generally present in notch, may be removed during processing

    Spotted knapweed (Centaurea stoebe) achenes

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  • Seed

    Size

    • Seed size similar to achene size

    Shape

    • Seed is oblong shaped

    Surface Texture

    • Seed surface is smooth

    Colour

    • Seed is light yellow coloured

    Other Features

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

    Size

    • The embryo fills the seed

    Shape

    • Embryo is spatulate, axial position

    Endosperm

    • Endosperm absent, nutritive tissue stored in the cotyledons

    Other Features

    • Cotyledons are fleshy and soft-textured

Identification Tips

CONSEILS POUR L’IDENTIFICATION

The achenes are generally distinguished from similar species by their relatively large side notch, a well-developed, persistent pappus, with light yellow coloured lines and tissue in the side notch.

Spotted knapweed (Centaurea stoebe) achene

Additional Botany Information

AUTRES RENSEIGNEMENTS BOTANIQUES

Flowers/Inflorescence

  • Flower heads oval shaped, flowers pink, purple or rarely white (FNA 1993+)
  • Involucral bracts are egg-shaped or oblong, with prominent nerves and dark tips
  • The bract edges near the top are divided into several narrow segments
  • The bracts protect the seeds as they develop, and disperse them through a hole at the end of the involucre (Watson and Renney 1974).

Centaurea stoebe flower (Rob Routledge, Sault College, Bugwood.org)

Similar Species

ESPÈCES SEMBLABLES

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 diffusa Lam. (diffuse knapweed)

C. diffusa achenes (length*: 1.4 – 2.6 mm; width: 0.7 – 1.1 mm) are shorter than C. stoebe, with a more shallow side notch. The pappus is generally short or lacking in C. diffusa (length: 0 – 0.5 mm, FNA 1993+) compared to C. stoebe.

*Note: minimum and maximum of 20 achenes in a normal range of this species using image measurement (ISMA 2020)

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Reference(s)

Référence(s)

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 15, 2020.

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/3127727 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.   https://www.idseed.org/authors/details/method_for_seed_size_measurement.html

Ochsmann, J. 2001. On the taxonomy of spotted knapweed (Centaurea stoebe L.). In: Smith, L., ed. Proceedings, 1st international knapweed symposium of the 21st century; 2001 March 15-16; Coeur d’Alene, ID. Albany, CA: U.S. Department of Agriculture, Agricultural Research Service: 33-41.

Sheley, R. L., Jacobs, J. S., and Carpinelli, M. F. 1998. Distribution, Biology, and Management of Diffuse Knapweed (Centaurea diffusa) and Spotted Knapweed (Centaurea maculosa) Weed Technology. 12: 353-362.

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.

Watson, A. K., and Renney , A. J. 1974. The biology of Canadian weeds 6. Centaurea diffusa and C. maculosa. Canadian Journal of Plant Science 54: 687-701.

Author(s)

AUTEUR(S)

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

Canadian Food Inspection Agency

contactus@idseed.org

Last updated
on 2023-03-27

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