Chilly, here's my read on "in" or "to," using a local example. Douglas fir is a native tree found in Alaska, British Columbia, Washington, Oregon, and California (that I know of, perhaps other states as well). I am comfortable stating that it is native IN my home state of Washington and IN the Pacific Northwest region, which does not limit it being native in other places. If I were to say it was native TO the PNW, that implies (to me) that it originated somewhere in this region - which likely is true in this example, but I don't have any specific source to back that up.
And as Eclayn so nicely illustrates, there are many plants which have naturalized in parts of the world that may be quite different from their point of origin. I don't know at what point a naturalized plant becomes native, or if that ever happens. I also find it rather difficult to locate reliable information on plant origins. Perhaps someone can guide me to a good website for that information?
