This time of year we get many calls regarding strange growths on tree trunks and tree limbs. What worries most people is that the growths at times appear to be completely covering the tree, and possibly smothering it.  The growth is called a Lichen (pronounced Like-en). The Lichen is an organism made of roughly 50% fungus, and 50% algae. It derives its nutrients strictly from the atmosphere, so it is not parasitic in nature. While it can look problematic, it is really just using the tree bark as a place to live.