A burl (American English) or bur or burr (used in all non-US English speaking countries) is a tree growth in which the grain has grown in a deformed manner. It is commonly found in the form of a rounded outgrowth on a tree trunk or branch that is filled with small knots from dormant buds.mboyna burl is a particularly expensive type of burl, costing $300.00 b/f to $72.00 per pound, much more than bigleaf maple burl, for example. It comes from padauk trees (Pterocarpus spp.) of Southeast Asia.