Canada Thistle, Cirsium arvense
(Cirsium arvense) Bloom Time: Summer – Fall (June – October) Location: prefers sun and moist, disturbed habitats such as old fields and roadsides. Also grows along lakeshores (general). Often found throughout many former agricultural fields on the prairie and around the perimeter of the Arb next to the roads (Arb). Family: Aster (Asteraceae) INVASIVE Physical Description: Flower heads are less than an inch across, and range from lavender to pale pink (occasionally white). Leaves are about 6 in. long and have yellow spines along the edges (pricklier than native thistles). This plant is a native to Europe and northern Asia, and was likely introduced to North America in the form of contaminated crop seeds in the 1600s. It is highly aggressive, outcompeting many native species by forming dense root mats on the ground. Populations can be controlled by hand-cutting, mowing, goats (selective grazing) and prescribed burns, yet none of these techniques harm the deep taproot of the plant.