If anyone has a copy of Decorated Firearms by Wallace Gusler and James Lavin, check out the section discussing stock wood. He did what he could to dispell the notion of root wood, burr walnut etc. Seems a lot of this started with Hayward (Art of the Gunmaker) and maybe even Lenk (The Flintlock). Even today I see numerous high end auction houses refer to what is obviously burl maple as burr walnut, rootwood, even suggesting it is "thuja" is common.
If I get a chance I may try to post the article mentioned above here. I don't think many have the book.
Jim