What a wonderful treasure you have! While I've never seen one, I've heard of quilts made from different types of tree bark (called bark cloth) but never saw one until now. You could contact some of the major quilt museums in your area to see if they can help you with the history of quilts made with bark cloth. I've heard that bark from different trees all over the world have been used in the making of quilts... I've just never seen any until now! Your quilt is amazing.... and I am trying so hard not to be envious because green is definitely not my color!