It's interesting about native species. Think about apple trees in the UK. They grow very well here, the climate is suited perfectly, they don't seem to be invasive (talking as a layperson here). Yet they were introduced about 2000 years ago by the Romans. Does that mean they're old enough to now count as native? I mean, if you go back far enough, everything came from somewhere else. Unless you're looking at a deep-sea vent where life very first evolved, then it has spread from somewhere else.
Maybe if I was a botanist or ecologist, I would know the actual answer. But I'm just a person who loves thinking about things in a philosophical way, without necessarily wanting to research in-depth answers for every little puzzle