Trees, Shrubs and Conifers: Cascara Buckthorn, 1 by Linnea

Linnea wrote:
I grew up knowing this useful medicinal tree as chittum, although Grandma was careful to teach me that it's real name was Cascara Buckthorn. Now, living in New Hampshire, I find an unknown shrub in our yard (well, ok, tamed wilderness more than yard) and the first thing that pops into my head is Cascara buckthorn. I usually do an initial id by my gut - that gives me somewhere to look in the book, to confirm it. But this time I said nah, it can't be, and tried to id it cold out of my books. No joy.

Finally, I give in and look up chittum. Lo and behold, it sounds just like what I have! I looked it up online, and the picture looks right. OK, I have cascara in my yard. But why? I have no idea. And, trying to look it up in the PDB leads to more confusion. the only plant with the right name has a different species name (Frangula as opposed to Rhamnus) and a very bad picture.

So, does anyone out there know what this is? and why are there two species both being called chittum and or cascara buckthorn?