U.S. Fish & Wildlife Service
America's National Wildlife Refuge System
Volunteers and Invasive Plants: Learning and Lending a Hand
Canada Thistle Origin
Native to southeast Europe and Asia, Canada thistle is believed to have been introduced to the United States by the 1700s as a contaminant of crop seed.
Numerous small flower heads
of Canada thistle
Infestation of Canada thistle with purple and white flower heads
Photo credit: MT Dept. of Agriculture (left)
S Dewey/Utah State Univ., www.forestryimages.org (right)
Reference
Whitson TD, ed. 2000. Weeds of the West. Jackson (WY): Western Society of Weed Science. 628 p.