Quote Originally Posted by Innuendo View Post
Yeah it is burl. People get it wrong all the time. It comes from the root burl underground at the base of the walnut tree. That is where the most interesting and intricate patterns are formed.

Edit: Learn something new everyday! http://en.wikipedia.org/wiki/Burl
Those big black lumps on the sides of box trees are burls as well. People cut them off and make furniture out of them. Maybe a Bently has real walnut burl, a Holden has plastic.