Cardamine pennsylvanica seems to be a quite variable species. This plant didn't seem noticably different from any number of other bittercress (which I think are also C. pennsylvanica) I have seen around town except that those ones (including some growing only a few feet away from this specimen) were barely larger than the knife at the bottom of the picture where as this one is several times larger. Maybe they have a recessive giantism gene or something.