In article , Nick Maclaren
writes

But, if I recall, there is also one which established itself in the
UK by natural hybridisation between an introduced species and a
native one. Now, that is clearly a good species, and the usual
interpretation is that it would be native to somewhere. But, if
not the UK, where? Cockaigne?


Spartina anglica, Senecio cambrensis, Senecio eboracensis, and probably
more (maybe a Rubus, Hieracium or Taraxacum microspecies or several).
--
Stewart Robert Hinsley