Weed Seed: Carduus nutans (Nodding thistle)

Family

Asteraceae

Common Name

Nodding thistle

Regulation

Primary Noxious, Class 2 in the Canadian Weed Seeds Order, 2016 under the Seeds Act.

Distribution

Canadian: Occurs across Canada with the exception of NT, NU, PE, YT (Brouillet et al. 2016Footnote 1).

Worldwide: Native to northern Africa, temperate Asia, and Europe. Introduced in North America, Chile, South Africa, Australia, New Zealand and beyond its native range in Europe (USDA-ARS 2016Footnote 2).

Duration of life cycle

Biennial

Seed or fruit type

Achene

Identification features

Size

  • Achene length: 2.4 - 3.8 mm
  • Achene width: 0.9 - 1.6 mm

Shape

  • Achene elongate, straight to slightly curved, tapering at the base and top is truncate

Surface Texture

  • Achene glossy surface, looks varnished

Colour

  • Achene light to dark golden brown; the base is canary yellow and a yellow band may occur below the collar

Other Features

  • Both longitudinal lines and transverse waves may be seen under the achene's varnish-like surface coating
  • The style peg at the top of achene is usually short and thick
  • Immature achenes may have a thin white pappus

Habitat and Crop Association

Old fields, pastures, rangelands, roadsides and disturbed areas (Desrochers et al. 1988Footnote 3, Darbyshire 2003Footnote 4).

General Information

Nodding thistle is believed to have arrived in eastern North America in ships' ballast, and introduced into Saskatchewan through rapeseed and dispersed along railway lines (Desrochers et al. 1988Footnote 3).

This species produces large numbers of seeds (11,000) per plant and may form dense stands in disturbed areas such as gravel pits, roadsides and overgrazed pasture (Desrochers et al. 1988Footnote 3).

Similar species

Spiny plumeless thistle (Carduus acanthoides)

  • Spiny plumeless thistle achenes (length: 2.5 - 3.0 mm) are generally shorter and paler than nodding thistle achenes. The achenes have the same elongate shape with a thick top peg, and both longitudinal and transverse lines occur on both species' achenes.
  • Spiny plumeless thistle does not have the canary yellow base of nodding thistle, and the lines on the surface stand out in relief, while the lines on the surface of nodding thistle are covered with a varnish-like coating.
  • Immature nodding thistle achenes may have lines that stand out from the surface, but they will have a yellow base.

Photos

Nodding thistle (Carduus nutans) achenes
Nodding thistle (Carduus nutans) achene
Nodding thistle (Carduus nutans) achene top peg
Nodding thistle (Carduus nutans) bottom of achene
Nodding thistle (Carduus nutans) achene
Nodding thistle (Carduus nutans) achenes

Similar species

Similar species: Spiny plumeless thistle (Carduus acanthoides) achenes
Similar species: Spiny plumeless thistle (Carduus acanthoides) achene
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