Lichens are not choosy about where they grow. You can find them on rocks, trees, fences, headstones, rain forests, deserts, and many other places. They will even survive in toxic dump sites. Lichens are symbiotic organisms, made up of a fungus partnered with a photosynthetic plant like alga. They take on many shapes and sizes, from leaf-like structures to draping feather-like formations. Lichens are sensitive to environmental disturbances, especially air pollution. Some lichens can be eaten, but they may be difficult to digest. Because of their vivid pigments, lichens are commonly used in dyes.