Lichens are pioneer plants that grow on rocks, trees, or on the ground where the leaf litter or grass has been disturbed. A symbiotic life form, they consist of an alliance between a fungus body and colonies of one-celled algae. The algae do the photosynthesizing and manufacture food. The fungus provides the structure and decomposes the rock underneath, thus aiding in soil formation.
There are three kinds and each finds its niche in the landscape. Crustose lichens attach to rock surfaces. They form crusts in broad round patches. The foliose varieties grow as green leaf-like lobes or plates attached to tree bark or rock. The hanging fruticose lichens are the most advanced types with stalked branches that sometimes resemble weird coral growths.
Lichens are tough and long-lived. They are highly resistant to cold, intense heat and to drought. Their growth is extremely slow. Lichens reproduce by means of spores from the fungi which combine with the algae, or by breaking off and reattaching in new locations.