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Canada Thistle (Cirsium arvense)         

Canada Thistle at the beginning of bloom.
Canada Thistle at the beginning of bloom.

Canada Thistle is a very serious invasive species of the genus Cirsium, native throughout Europe, Asia and northern Africa. This plant is cited as a noxious weed in several countries; for example Brazil and the United States.

It is a tall herbaceous perennial plant, forming an extensive underground root system that sends up numerous erect stems each spring, reaching 1-2 m tall; the stems often lie partly flat by summer but can stay erect if supported by other vegetation. The leaves are very spiny, lobed, up to 15-20 cm long and 2-3 cm broad (smaller on the upper part of the flower stem). The flowers are 1-2 cm diameter, pink-purple, with all the florets of similar form (no division into disc and ray florets). The seeds are 4-5 mm long, with a downy pappus which assists in wind dispersal.

Canada Thistle is used as a food plant by the Engrailed, a species of moth.

Several other names have been applied to the species, including Field Thistle, and the very confusing "Canada Thistle" (it is not a native of Canada, being an introduction there).(From Wikipedia)

Canada Thistle rosettes.
Canada Thistle rosettes.

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