I've spent ages trying to identify these flowers and this seems to be it although how a North American species got to my local wood I have no idea!
No interactions present.
Probably arrived as dumped garden waste.
seed is fairly small so cold easily be carried on clothing or blown for short distances.
That would make sense. There is a housing estate not far away although dare I say not many of the gardens look well cared for. Dumping in the wood is a problem though.
Certificate in Contemporary Science (Open)
Lat/Lng: 51.418800368814, -0.95684051513672
OS grid ref: SU726693