Canada Thistle (Cirsium arvense): purple Minnesota wildflowers

Canada Thistle

Plant Info
Also known as:	Field Thistle
Scientific name:	Cirsium arvense
Family:	Aster (Asteraceae)
Life cycle:	perennial
Origin:	Europe
Habitat:	sun; old fields, along roads, waste areas
Bloom season:	summer
Plant height:	3 to 5 feet
USDA PLANTS database:	Minnesota county distribution map
Spotted in Ramsey County at:	Long Lake Regional Park Vadnais/Snail Lake Regional Park

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Flower:: Flower heads are ¾ inch across, lavender to pale pink or sometimes white. The bracts are flat, except for the tip which peels back away from the flower head. The bract tips are pointed, but not spined, and often a purplish color. One plant can have numerous flower heads, branching off the main stem near the top of the plant.
Leaves and stem:: Leaves are up to 6 inches long with no leaf stem and yellow spines scattered along the wavy edges. The lower leaves are up to 2½ inches across and deeply lobed, with a spine at the tip of each lobe. The upper leaves are more narrow, and generally more toothed than lobed. Leaves may be somewhat hairy on the underside. The main stem is light green, slightly ridged and may have scattered hairs but is not usually spiny.
Notes:: Canada Thistle is on the prohibited noxious weed list for Minnesota. It can form large colonies and crowd out native plants. Canada Thistle is fairly easy to identify from the numerous small flower heads, and bracts that have no spines.

Photos taken at Long Lake Regional Park, New Brighton, MN, June 2006 and June 2007

Have you seen this plant in Ramsey County, or have any other comments about it?