Lichen on the branch of an apple tree

Information from the WWW
Scotland has over 1500 species of Lichen. Clean air, diverse habitats, relatively cool summers and mild winters all contribute to this diversity. Each type of lichen is a successful partnership between two species, a fungus and an alga (or blue-green alga). The fungus provides a protective home for the alga and in return, the alga produces food for the fungus from sunshine, water and air.

Lichens grow very slowly, some less than a millimetre per year, and can take many years to establish in new locations.