Canada thistle

Asterales > Asteraceae > Cirsium arvense (L.) Scop.
Synonym(s): Californian thistle, creeping thistle, field thistle

Canada thistle is a tall, erect, spiny, perennial, herbaceous plant that grows to 4 ft. (1.2 m) tall. It has an extensive creeping rootstock. The leaves are lance-shaped, irregularly lobed, 2-6 in. (5-15 cm) long with prickly margins. The stems are ridged and hairy. The flowers are purple to white and can be up to 0.5 in. (1.8 cm) in diameter. Flowering occurs in late June to August. The small fruit, called achenes, are 1 to 1.5 in. (2.5-3.8 cm) long and have a feathery pappus which allows them to be dispersed further by wind. Numerous species of thistle occur in North America, and while some are invasive, many are native. Often the species are difficult to distinguish. Canada thistle can invade a variety of open habitats including prairies, savannas, fields, pastures, wet meadows and open forests. It forms dense stands which can shade out and displace native vegetation. Once established it spreads rapidly and is difficult to remove. Canada thistle is native to Europe and Asia and was accidentally introduced to North America in the 1600s.


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);
Lynn Sosnoskie, University of Georgia, Bugwood.org
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Foliage;
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Foliage;
Mary Ellen (Mel) Harte, , Bugwood.org
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Flower(s);
Steve Dewey, Utah State University, Bugwood.org
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Flower(s); Purple and (rare) white flowers in the same field
Steve Dewey, Utah State University, Bugwood.org
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Flower(s); In a forested setting. South Dakota
Chris Evans, River to River CWMA, Bugwood.org
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Flower(s);
Mary Ellen (Mel) Harte, , Bugwood.org
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Flower(s); Female flower heads
Richard Old, XID Services, Inc., Bugwood.org
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Flower(s);
Michael Shephard, USDA Forest Service, Bugwood.org
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Flower(s); Male flower heads
Richard Old, XID Services, Inc., Bugwood.org
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Flower(s); Male flower heads
Richard Old, XID Services, Inc., Bugwood.org
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Fruit(s); Female flower heads
Richard Old, XID Services, Inc., Bugwood.org
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Plant(s);
Dan Tenaglia, Missouriplants.com, Bugwood.org
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Plant(s);
Mary Ellen (Mel) Harte, , Bugwood.org
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Plant(s);
Peggy Greb, USDA Agricultural Research Service, Bugwood.org
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Plant(s);
Mary Ellen (Mel) Harte, , Bugwood.org
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Plant(s);
UAF Cooperative Extension Archive, University of Alaska - Fairbanks, Bugwood.org
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Infestation;
UAF Cooperative Extension Archive, University of Alaska - Fairbanks, Bugwood.org
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Infestation; In a pasture
Steve Dewey, Utah State University, Bugwood.org
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Infestation; in canola (Rape seed) field near Consort, Alberta
Alec McClay, McClay Ecoscience, Bugwood.org
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Diagram or Graphic; USDA NRCS. Wetland flora: Field office illustrated guide to plant species. USDA Natural Resources Conservation Service.
USDA PLANTS Database, 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: 553.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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Invasive Reference(s):

Check Invasive.org for most current lists.
  • Alabama - IPC List
  • Alaska - Noxious Weed Law
  • Arizona - Noxious Weed Law
  • California - Noxious Weed Law
  • California - Invasive Plant Inventory
  • Colorado - Noxious Weed Law
  • Connecticut - Noxious Weed Law
  • Delaware - Noxious Weed Law
  • Illinois - Noxious Weed Law
  • Iowa - Noxious Weed Law
  • Indiana - Noxious Weed Law
  • Kansas - Noxious Weed Law
  • Kentucky - EPPC List
  • Kentucky - Noxious Weed Law
  • Maryland - Noxious Weed Law
  • Michigan - Noxious Weed Law
  • Minnesota - Noxious Weed Law
  • Missouri - Noxious Weed Law
  • Montana - Noxious Weed Law
  • Nebraska - Noxious Weed Law
  • New Mexico - Noxious Weed Law
  • Nevada - Noxious Weed Law
  • North Carolina - Noxious Weed Law
  • North Dakota - Noxious Weed Law
  • Ohio - Noxious Weed Law
  • Oklahoma - Noxious Weed Law
  • Oregon - Noxious Weed Law
  • Pennsylvania - Noxious Weed Law
  • Rhode Island - Noxious Weed Law
  • Rhode Island - Invasive Species Council List
  • South Dakota - Noxious Weed Law
  • Tennessee - EPPC List
  • Utah - Noxious Weed Law
  • Virginia - Invasive Alien Plant Species
  • Washington - Noxious Weed Law
  • Wisconsin - Noxious Weed Law
  • Wyonming - Noxious Weed Law
  • Mid-Atlantic - EPPC List
  • 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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