Lichens are some of the most amazing organisms on the Earth. A lichen is a stable, ecologically obligate, self-supporting mutualism between an exhabitant fungus (the mycobiont) and one or more inhabitant, extracellulary located unicellular or filamentous phototrophic partners (the photobiont: alga or cyanobacterium). There are about 18500 known species. Lichenized fungi occur in a wide range of habitats: from arctic to tropical regions, from the plains to the highest mountains, and from the aquatic to the xeric conditions. Lichens can be found on or within rocks, on soil, on tree trunks and shrubs, on the surface of living leaves and on any stationary, undisturbed man-made surfaces such as glass, metal, wooden fence, concrete, mortar, brick, plastic. They are pioneers and famous bioindicators.