|Rosebay Willowherb seeds, Epilobium angustifolium. High Elms Country Park, 22 August 2011.|
It is certainly an early urban coloniser. In London, after World War II, it grew in the craters where buildings had been blown up in the Blitz. Where I grew up, near Newcastle, we often saw it where rows of houses had been demolished.
The flower of this species is what the crab spider I posted recently was sitting on.