Lichens are the result of symbiosis ..

Lichen is the result of a symbiotic relationship between algae (usually green, or cyanobacteria) and fungi (mainly ascomycetes and basidiomycetes). Lichens are found all over the world and in various environmental conditions. They can colonize a wide variety of surfaces and are often found on tree bark, outcrops, and as part of the biological soil crust. Lichens have been used by humans as food and as sources for medicine and dyes. They also provide two-thirds of the food for the caribou and reindeer that roam the far northern ridges.