Scotch thistle

Asterales > Asteraceae > Onopordum acanthium L.
Synonym(s): cotton thistle, heraldic thistle, Scotch cottonthistle

Scotch thistle is a biennial herb native to Eurasia. Plants can grow up to 8 ft. (2.4 m) tall and 6 ft. (1.8 m) wide. Stems are up to 4 in. (10.2 cm) wide at the base and are marked by prominent, spiny wings along the entire length. Leaves are broadly elliptic, 3.9-19.7 in. (10-50 cm) long, up to 12 in. (30.5 cm) wide with margins marked by large spines. Flowering occurs from July to September, when flowers develop in globe shaped flower heads. Flower heads are purple and up to 2 in. (5.1 cm) in diameter. Fruits are 0.2 in. (4-5 mm) long, smooth achenes. Scotch thistle occurs along roadsides, in fields, pastures, rangelands, riparian areas and other disturbed sites with high soil moisture.


Identification, Biology, Control and Management Resources

  • Weeds of the Week - USDA Forest Service, Northeastern Area, Forest Health Protection

Selected Images from Invasive.org

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Plant(s); Rosette
Steve Dewey, Utah State University, Bugwood.org
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Plant(s);
Steve Dewey, Utah State University, Bugwood.org
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Feature(s); Flower and foliage
Steve Dewey, Utah State University, Bugwood.org
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Flower(s);
Eric Coombs, Oregon Department of Agriculture, Bugwood.org
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Flower(s);
Steve Dewey, Utah State University, Bugwood.org
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Plant(s); in flower
Steve Dewey, Utah State University, Bugwood.org
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Plant(s);
Steve Dewey, Utah State University, Bugwood.org
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Plant(s);
Steve Dewey, Utah State University, Bugwood.org
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Plant(s);
Steve Dewey, Utah State University, Bugwood.org
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Infestation;
Steve Dewey, Utah State University, Bugwood.org
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Infestation; on river bank, seeds travel down water way
Vince Belleci, , Bugwood.org
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Infestation;
Steve Dewey, Utah State University, Bugwood.org
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Control; Volunteer weed control programs, such as the annual Scotch Thistle Day, help teach young people about the impact of invasive plants on native ecosystems and agricultural production.
Steve Dewey, Utah State University, Bugwood.org
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Fruit(s);
Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org
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Diagram or Graphic; Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 3: 556.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Invasive Reference(s):

Check Invasive.org for most current lists.
  • Arizona - Noxious Weed Law
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Colorado - Noxious Weed Law
  • Connecticut - Noxious Weed Law
  • Missouri - Noxious Weed Law
  • New Mexico - Noxious Weed Law
  • Nevada - Noxious Weed Law
  • Oklahoma - Noxious Weed Law
  • Oregon - Noxious Weed Law
  • Texas - Invasive Plant List
  • Utah - Noxious Weed Law
  • Washington - Noxious Weed Law
  • Wyonming - Noxious Weed Law
  • Invasive Plants: Western North America
  • Invasive Plants: Guide to Identification and the Impacts and Control of Common North American Species
  • Invasive Plants of the Upper Midwest
  • Invasive Plant Atlas of New England


External Links


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