Tree features are the various characteristics of a tree that make it unique. The BARK is the outer layer of the tree, which can be rough or smooth and can vary in color. A BURL is a growth on the trunk or branches of a tree, often caused by an injury or infection. Knots are protrusions on the surface of the tree, usually caused by branches that have grown together. Knar is a term used to describe the gnarled, twisted shape of a tree's trunk or branches. Lastly, limbs are the branches of a tree, which can be thin or thick and can range in length.