What is a lichen? Lichens are a symbiotic relationship between algae, fungus and yeast. There are over 500 different species of lichen in Mount Rainier National Park. Advances in DNA testing have necessitated a number of changes to lichen taxonomy. The names given here are current as of January 2020.
Lichens generally can be grouped by growth form, including foliose, fruticose, and crustose forms, as described in the sections below. Some species are a blend of two forms.
A special vocabulary is used when discussing lichen structure. The main body of the lichen is referred to as its thallus, and the fruiting bodies are called apothecia (singular: apothecium).