Hardwood burls are hard, woody rounded protrusions that form on trunks and branches of hardwood trees including maple, oak and cherry. Furniture makers use large burls of trees such as black walnut and northern red oak for decorative veneers. Manufacturers often consider burls as grade defects in logs.
Hardwood trees, which are plentiful in the United States, have broad leaves, go dormant in winter and typically produce nuts or fruit. The wood grain under a true burl has a curly, wavy or bird's-eye effect in the burl stem and the wood around it. The unusual look and shape of true burls make them valuable, and wood crafters use them to produce items such as trays, fruit bowls and wall decorations.