renaissance poisson

Ah - ruderal. I didn't know there was a word for that; thanks.
Pretty much all thistles are edible. They've got the thorns for protection, so they don't need to waste energy on toxin production. I haven't had canada thistle either, but milk thistle is tasty. The stalks are like salty tender celery, after you strip off the outer bits. There was a thistle that grew in profusion in the East Bay (SF) that I suspect was a cross between artichoke and milk thistle. Or it might just have been artichoke gone wild. I harvested the buds, once, and steamed and ate them like artichokes, except I didn't bother doing the leaf-by-leaf thing because they were tiny (about 2 cm across). Tasted great.