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This contribution on Cirsium arvense (L.) Scop., Canada thistle (Compositae) is part of a series which presents biological information on plants that are weedy in Canada. Canada thistle is a serious weed of agricultural land of all types and is one of the most serious weeds of temperate regions. Introduced from Europe in the 17th century, it now occurs in all provinces of Canada.
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Robert E. Moore (1975) studied this question.
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