Mahonia or Berberis?
Botanists are still trying to figure out if Berberis and Mahonia should be in the same genus or not. They've been niggling at things for a long time now.
The discussion goes something like this:
During a botanical conference years ago, one botanist got up and said, "looky here, these have spiny stems, right? These have spiny leaves. Clearly very different from each other."
Thus, Berberis and Mahonia.
The next conference was a few years down the line, and another botanist got up and said, "Can't you tell that the flowers are close to identical? They're all Berberis," and he goes off, muttering 'dimwits...'.
So they were all Berberis again.
A few years later, another conference, and another botanist got up and said, "Braindead morons, the lot of you. Check this, spiny leaf, spiny stem. Blue berries, red berries. The same genus? Ha!"
And they were Mahonia and Berberis again.
Another couple years go by, another botanical conference, and another botanist got up and said "Wheee, guys, check this species! It's got the leaf of Mahonia and the stem of Berberis (..or something such), they must be the same genus!"
And they were all Berberis again.
They're still slugging it out. Currently they're all Berberis. I think. Not that it actually matters: if they're lumped now they'll be divided again within the next few years. And lumped again a few years later.
Herbalists have long known that the yellow roots and rootbarks of Mahonia and Berberis are close to identical in their medicinal effects. Mahonia has perhaps a tad more variety in its uses, but getting worked up over that rather unimportant point might make us look just as silly as the botanists, and we don't want that, eh?