For years, people kept telling me they had Oregon grape, Berberis aquifolium (syn. Mahonia aquifolium), and that it was a native species. This seemed unlikely, since I live in the southeast, and Oregon is ... elsewhere. So I looked it up and, sure enough, Oregon grape isn't native to the southeast. Furthermore, it seemed unlikely that a plant native to northwest was thriving in the southeast, and I had also noticed it naturalizing in the woods.

So it turns out that practically nobody here actually has Oregon grape. Instead, they have leatherleaf mahonia, Berberis bealei, a species from east Asia that looks remarkably similar to Oregon grape. Moreover, it's increasingly becoming invasive in much of the southeast.

I'm guessing that leatherleaf mahonia is being sold as Oregon grape, and people are being told that it's "native" because it occupies the same continent.