Lichens are not individual organisms; they are composite organisms that comprise of fungus and a photosynthetic organism that share a symbiotic relationship. The photosynthetic organism may either be green alga or nostoc. Interestingly, the physiological and biochemical characteristics of lichens are completely different from fungus or green alga. This uniqueness of lichens allows them to survive in the harshest of environments, such as the scorching deserts of Gobi and the frigid tundra lands of the Arctic. They can also be found in friendlier environments such as rainforests and temperate woodlands.