In Ireland I was struck by the ubiquity of non-native plants in the Irish countryside. It took me a while to realize that the lush green grass that lined nearly every lane was in fact the young foliage of crocosmia which must have completely overwhelmed the native species that grew there previously. I suspect that the naturalised Olearia bushes aren’t a particular threat and the fuchsias appear to coexist happily with their native neighbours, but the two plants that seem to be gaining and increasing foothold without any visible attempt to control them are Japanese knotweed and phormium – I actually saw the former planted as a hedge along a roadside and the latter is popular as an impenetrable and stock proof boundary along field margins where they look very ugly and reach up 10ft high and wide.
Olearia
Japanese Knotweed Hedge!