Sorry to disappoint all who think this is unique idea but it has been done before although that takes nothing away from the docs pen, it is a fine piece indeed.
Your so called Buckeye Burr is only root from conker tree (Horse Chestnut). Or if ya wanna do it the Yankee way (Aesculus californica, California Buckeye Burl or California Horse-chestnut).
I think we all went through a root phase a few years ago turning Hydrangea and rose roots it is wood after all init?
Nice pen Doc lovely finish good pic init?