Douglas County Conservation District

SERVING LANDOWNERS IN DOUGLAS COUNTY COLORADO FOR OVER 56 YEARS

     PO BOX 688, 7519A E HWY 86, FRANKTOWN, CO 80116   303-218-2622

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Canada Thistle
Cirsium arvense                                    Fact Sheet

Stems are 1 to 4' tall, ridged, branching above.  Leaves are alternate, oblong or lance-shaped, divided into spiny-topped irregular lobes.  Flowers are unisexual, on separate plants; flowers purple (occasionally white) in heads 1/2 to 3/4 inch in diameter.  Fruits are about 1/8 inch long, somewhat flattened, brownish, with a tuft of hairs at the top.

Differs from other species of the true thistle in that there are male and female flower heads, and these are on separate plants.  By asexual reproduction, it is possible that a colony of male plants would produce no fruits, but still maintain itself.  Flowering occurs during July and August.