Weed Seed: Centaurea iberica (Iberian starthistle)

Invasive Plant - Iberian Starthistle (Centaurea iberica)

Family

Asteraceae

Common Name

Iberian starthistle

Regulation

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.

Listed on the List of Pests Regulated by Canada established under the Plant Protection Act.

Distribution

Canadian: Absent from Canada (Brouillet et al. 2016Footnote 1).

Worldwide: Native to areas from eastern Europe to extreme western China and India. Introduced in the United States, where it has been found in the Pacific states, Wyoming and Kansas (CFIA 2012Footnote 2). Also introduced in Argentina and outside of its native range in Europe (CABI 2016Footnote 3).

Duration of Life Cycle

Biennial; may behave as an annual or short-lived perennial

Seed or Fruit Type

Achene

Identification Features

Size

  • Achene length: 3.0 - 4.3 mm
  • Achene width: 1.5 - 2.0 mm
  • Pappus length: 1.0 - 3.3 mm

Shape

  • Oblong-shaped achene with rounded bottom and flat top, compressed; large notch near the base along the narrow edge

Surface Texture

  • Achene is smooth with satin sheen

Colour

  • Achene is white and brown-streaked; variable in colouration

Other Features

  • White pappus is composed of flat bristles of variable lengths
  • Outer bristles of pappus tend to be shortest, increasing in length towards the inside

Habitat and Crop Association

Fields, pastures, rangelands, woodlands, shrublands, banks of watercourses, roadsides and disturbed areas ( DiTomaso and Healy 2007Footnote 4, CABI 2016Footnote 3). In the United States, it is highly competitive along roadsides and in rangelands.

General Information

Iberian starthistle was accidently introduced into the western United States, from where it has since spread, most notably in the 1920s (DiTomaso and Healy 2007Footnote 4) and the 1950s (Graham and Johnson 2003Footnote 5).

Similar Species

Purple starthistle (Centaurea calcitrapa)

  • The achenes of purple starthistle are a similar size, oblong shape and smooth surface with reddish-brown streaks that appear like wood-grain.
  • The achenes of purple starthistle have a smaller basal notch, dull surface and lack a pappus compared to Iberian starthistle.

Photos

Iberian starthistle (Centaurea iberica) achene
Iberian starthistle (Centaurea iberica) achene, side view
Iberian starthistle (Centaurea iberica) achene, top-down view
Iberian starthistle (Centaurea iberica) achene, basal notch

Similar species

Similar species: Purple starthistle (Centaurea calcitrapa) achenes
Similar species: Purple starthistle (Centaurea calcitrapa) achene
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