Those odd looking bark covered knobs or lumps on the trunks or branches of trees are called burls. They can form on any type of tree and possibly develop when something irritates or stresses the tree, such as an injury, a fungus or insect activity. Tree burls usually do not kill a tree but might affect the health of the tree in the long run. On wild cherry trees they may be caused by a fungus called Black Knot. These irregular, knobby looking growths on the twigs, branches and sometimes the trunks of cherry trees produce spores that are spread by wind or rain during the damp spring season. Another odd looking object clinging to the side of a tree might be a shelf fungus, also called bracket fungus. They come in many different sizes, shapes and colors and can consist of a single body or form rows or groupings. They play an important role in the process of wood decay and nutrient recycling on dead trees, and when on live trees, may start an area of rot where they attach. Those white, green, yellow, gray or orange blotches on the branches or trunks of trees are likely a type of lichen. Lichens are a combination of a fungus and an algae or cyanobacteria (a type of bacteria that is able to complete photosynthesis) and exist in many shapes and forms. Lichens don’t harm the objects that they attach to and they grow very slowly. Lichens can also be found on, rocks, gravestones, and old benches.