You can identify three general types of lichens by their shape and appearance. The best known local examples of fruticose lichens are British soldiers, old man's beard and reindeer lichen. Fruticose lichens are often the first to disappear when a natural habitat is disrupted. Probably the most common type of lichen in Missouri is the foliose lichen. These are flat, typically green or gray lichens that can be abundant on trees and rocks, especially in the Ozarks.
Crustose lichens are the most diverse and least noticed group of lichens in Missouri.
Just as their name implies, crustose lichens often look like a thin crust on rocks, soil, trees, fenceposts, shingles and old, rusted iron on bridges. Some crustose lichens even grow inside rocks, occupying the microscopic spaces between rock crystals. Most crustose lichens are small and drab and require a microscope for identification. A few types of crustose lichens are among our most adaptable species and even thrive on concrete in downtown St. Louis and Kansas City. Important yet tiny, colorful but often overlooked, lichens play an unusual role in our environment and in human consciousness.