| Canada thistle |
USDA PLANTS Symbol: CIAR4 USDA ARS GRIN: 100755 ITIS: 36335 NAPIS: PBFAWBB |
| Cirsium arvense (L.) Scop. | |
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Taxonomic Rank: Magnoliopsida: Asterales: Asteraceae |
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| 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. |
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Identification, Biology, Control and Management Resources
- Weed of the Week - USDA Forest Service
- Federal Noxious Weed Disseminules of the U.S. - USDA-APHIS
- Fire Effects Information System - USDA Forest Service
- Invasive Plant Atlas of New England - University of Connecticut
- Element Stewardship Abstract - The Nature Conservancy
- Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
- Plant Invaders of Mid-Atlantic Natural Areas - National Park Service and U.S. Fish and Wildlife Service
- Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance
- Fact Sheet - Pennsylvania Dept. of Conservation and Natural Resources
| Selected Images from Invasive.org | View All Images at Invasive.org |
 Foliage; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage |
 Foliage; Mary Ellen (Mel) Harte, , Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Purple and (rare) white flowers in the same field Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); In a forested setting. South Dakota Chris Evans, River to River CWMA, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Mary Ellen (Mel) Harte, , Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Female flower heads Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Michael Shephard, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Male flower heads Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Male flower heads Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage |
 Fruit(s); Female flower heads Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Dan Tenaglia, Missouriplants.com, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Mary Ellen (Mel) Harte, , Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Peggy Greb, USDA Agricultural Research Service, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Mary Ellen (Mel) Harte, , Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); UAF Cooperative Extension Archive, University of Alaska - Fairbanks, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; UAF Cooperative Extension Archive, University of Alaska - Fairbanks, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; In a pasture Steve Dewey, Utah State University, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; in canola (Rape seed) field near Consort, Alberta Alec McClay, McClay Ecoscience, Bugwood.org Additional Resolutions & Image Usage |
 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 Additional Resolutions & Image Usage |
 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 Additional Resolutions & Image Usage |
Taxonomic References:
- USDA, NRCS. 2001. The PLANTS Database, Version 3.1, National Plant Data Center, Baton Rouge, LA 70874-4490 USA.
Invasive Listing Sources:
- City of Ann Arbor Michigan Parks and Recreation
- Commonwealth of Pennsylvania, Department of Conservation and Natural Resources, 1994.
- Connecticut Invasive Plant Working Group
- Delaware Natural Resources and Environmental Control, 2004
- Faith Campbell, 1998. Plants that Hog the Garden: Invasive Plants in the United States. Fine Gardening Online
- Forest Service-Alaska, 2004
- Hoffman, R. & K. Kearns, Eds. 1997. Wisconsin manual of control recommendations for ecologically invasive plants. Wisconsin Dept. Natural Resources, Bureau of Endangered Resources. Madison, Wisconsin. 102pp.
- Indiana Native Plant and Wildflower Society
- Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
- John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
- Maryland Cooperative Extension Service. 2003. Invasive Plant Control in Maryland. Home and Garden Information Center, Home and Garden Mimeo HG88. 4 pp.
- Maryland Department of Natural Resources, 1994
- Mid-Atlantic Exotic Pest Plant Council, 2005
- Missouri Department of Conservation,
- National Wildlife Refuge Association, Silent Invasion: A Call to Action from the National Wildlife Refuge Association, 2002. Washington DC. 17 pp.
- New Jersey Department of Agriculture, Division of Plant Industry, 2004
- Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
- Pacific Northwest Exotic Pest Plant Council, 1998
- Rhode Island Natural History Society,
- Virginia Department of Conservation and Recreation, 1999.
- WeedUS - Database of Plants Invading Natural Areas in the United States
- Alaska Noxious Weeds
- Alabama Invasive Plant Council
- Arizona Noxious Weeds
- California Invasive Plant Council
- California Noxious Weeds
- Colorado Noxious Weeds
- Connecticut Noxious Weeds
- Delaware Noxious Weeds
- Iowa Noxious Weeds
- Idaho Noxious Weeds
- Illinois Noxious Weeds
- Indiana Noxious Weeds
- Kansas Noxious Weeds
- Kentucky Exotic Pest Plant Council Significant Threat
- Kentucky Noxious Weeds
- Maryland Noxious Weeds
- Michigan Noxious Weeds
- Minnesota Noxious Weeds
- Missouri Noxious Weeds
- Montana Noxious Weeds
- North Carolina Noxious Weeds Class B
- North Dakota Noxious Weeds
- Nebraska Noxious Weeds
- New Mexico Noxious Weeds
- Nevada Noxious Weeds
- Ohio Noxious Weeds
- Oklahoma Noxious Weeds
- Oregon Noxious Weeds
- Pennsylvania Noxious Weeds
- South Dakota Noxious Weeds
- Tennessee Exotic Pest Plant Council Significant Threat
- Utah Noxious Weeds
- Washington Noxious Weeds
- Wisconsin Noxious Weeds
- Wyoming Noxious Weeds
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