ROADWEEDS OF THE UPPER PENINSULA
|Thistles (Cirsium spp.)|
Thistles are truly unpleasant plants to have around and the most obnoxious specimens are exotic species that readily invade native habitats. The three worst species are bull thistle (C.vulgare), European swamp thistle (C. palustre), and Canada thistle (C. arvense). Note that "Canada" thistle is not an exotic from Canada, it's from the Mediterranean region. Bull and European swamp thistle are bienniels, meaning they flower once every two years. A little glyphosate herbicide readily eliminates the first-year rosettes. Failing that, it's rather fun to go "thistle-whacking" on those nice summer days when the tall flower heads are present. A good machete will prevent the plants from forming seed and reduce the amount of seed floating across the landscape. However, be careful not to kill our native species, especially Pitcher's thistle (C. pitcheri) found along the Great Lakes sand dunes. It's on Michigan's "threatened" plant list.
Return to the Purple Flower Page, or to the Michigan Invasive Plant Council home page.
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