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Canada
Thistle - Cirsium arvense
Family: Asteraceae
Description
This prickly, perennial herb is dioceous, meaning that plants are either male or female, but do not have both parts on any one plant. Usually any given stand is one or the other. Males of course do not produce seeds.
This plant can easily be distinguished from other thistles, because of its smaller size. Of course, its difficult to distinguish them if you're not used to looking at thistles. However, the most common mistake is that people seem to misidentify it as spotted knapweed (something I found in the official guide to the Flowers of Grand Teton National Park). Spotted Knapweed however does not have the same spiney nature of this plant, even thought he flowers do look very similar.
Other similar thistles: Bull Thistle, Musk Thistle.
Interesting facts
The actual name, Canada Thistle, is a bit misleading, because it is not native to Canada, nor anywhere else in North America for that matter. It came over from Europe and now is one of the worst weeds in the Northern United States. Another name for Canada Thistle is Creeping Thistle.
VIDEO
Links to more information
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Pictures of Canada Thistle - Rutgers University
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CSU - Information and Control - A great source of information on the plant and any sort of control procedures used on it.
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NPS - Information - good overview of distribution, biology, and management options.
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Growth and Control information - very detailed information with statistics from the University of Nebraska.
Website, video, and graphics by Rob Nelson
For more information on this plant or management please contact US Army Corp of Engineers
