this weekend was the Staudenmarkt/perennial market at the botanical garden.  I was hoping to explore the garden itself, but ended up so laden down with bags, that I only stopped to take a few photos, this was one of them.  there were so many people there that I couldn't get close enough to get a name, but I am fairly sure that it is a North American native as it was in that part of the garden.   They come up in marshy land.