Lichen

Lichen is a simple, slow-growing plant that gives a crusty, leafy feeling when touched and forms on trees, rocks, or walls. In the picture, the lichen grew off of the tree and formed the green spots on the bark of the tree. The purpose of lichen is to absorb everything in the air which allows scientists to determine air pollution in the area by extracting molecular compounds from the lichen and if grown on rocks, it contributes to the breakdown of rock into soil.