Other names: European Swamp Thistle
The European Marsh Thistle (Cirsium palustre) is an aggressive invasive species of wetlands in the United States. While working is some pristine wetlands often the only invader I have found has been this species. The European Marsh Thistle seeds have parachutes, just like the common dandelion, and can be carried by the wind for many miles. Like most of the aggressive invaders of our wetlands it is typically the tallest plant around. However it does not form the dense stands like invasive cattails or phragmites, but can be abundant.
The USDA has a nice review of this thistle.