Coincidentally, on the sedging trip to Ramsdell, I saw this blackberry. It keys to Rubus setosus in Michigan Flora, as did the pink one on the wildflower page. MF notes that plants in this complex are similar to R. hispidus, the swamp dewberry. With this one I wasn't seeing that. They seemed much more like other blackberries. They also note that, "This complex, unfortunately, seems to be a repository for plants with the armature of R. hispidus but differing in enough other characters so as not to fit comfortably in that complex." No comfort with blackberries, as anyone knows who has tried to walk through the patch!