Indeed. When it is something we do not like and consider 'foreign', we call it invasive. When the same thing is considered native, even if its only here for a couple of hundred years, we call it a pioneer species.

Truth is, plants move around the world all the time even without the help of humans, and are relatively quick to adapt. Invasive species exploit a niche in the ecosystem that hasn't been filled yet, and are extremely useful in building up the system. Eventually the system will find a new balance, except when humans keep disturbing it.

Sometimes I think that 'invasive weeds threaten native plants' is the ecological equivalent of 'foreigners taking our jobs'. Preservation turning into botanical racism.