I have a thistle family that I have cultivated, it sounds like it could be as invasive as the Canada Thistle. This one is called Sea Holly, (Eryngium). I tried to transplant yesterday some of its seedlings that have germinated nearby the mother plants. I cannot believe the deep root on them, couldn't get to the bottom. Transplanted anyways, we'll see if they take off.
I don't dare to let this thistle to self-seed, there are literally thousands upon thousands of tiny steel blue, round thistle heads and I could see my entire property invaded, such as this Canada Thistle that has obvioulsy almost become a "noxious weed", so they call things of this nature. Oh brother, have a wonderful day, beautiful life. Cindi