Invasive Plants of Wisconsin
Carduus nutans is a large, invasive alilen species of sunny, disturbed sites. The stiff, spiny stems make it an unpleasant plant to deal with. The flower heads are very large, often 2 or 3 inches in diameter and they tend to bend over or "nod" as they mature. The stems are reported to reach 2 meters in height and the Brown County plants often exceed 1.5 meters. Carduus nutans is a biennial, not producing flowers until the second year, after which it dies. It usually begins to flower about mid-June.
Carduus nutans appears to have entered Brown County as a contaminant of the cover crops planted to stabilize the right-of-way after construction of Highway I-43 in the City of Green Bay (in 1979 or 1980 as I recall) and it was first reported in flower in June of 1981. It's greatest concentration is still along the banks where other streets pass under I-43, but recently it appears to be spreading into other areas (e.g. the area near the I-43 ramps near University Avenue in northeastern Green Bay).