Lichens of the Sierra Nevada have been little studied.[1] A lichen is a composite organism consisting of a fungus (the mycobiont) and a photosynthetic partner (the photobiont or phycobiont) growing together in a symbiotic relationship.
One classification of Sierra Nevada lichens is according to functional groups, by the National Park Service.[1] These functional groups overlap with each other. These include forage lichens (eaten by animals), nitrogen fixers (can take nitrogen molecules from the air and attach them to other molecules), acidophiles (acid loving lichens), wolf lichens, crustose lichens on rock, crustose lichens on bark and wood, biotic soil crusts, aquatic lichens, other green algal macrolichens, and pin lichens (calicoids)”.[1]: 2 These functional groups overlap.[1]: 4 In this article, we include wolf lichens as a subsection of crustose lichens growing on wood.