What is Map lichen?
{{Taxobox | name = ''Rhizocarpon geographicum'' | image = Rhizocarpon geographicum on quartz.jpg | image_width = 240px | regnum = [[Fungus|Fungi]] | divisio = [[Ascomycota]] | classis = [[Lecanoromycetes]] | ordo = [[Lecanorales]] | familia = [[Rhizocarpaceae]] | genus = ''[[Rhizocarpon]]'' | species = '''''R. geographicum''''' | binomial = ''Rhizocarpon geographicum'' | binomial_authority = ([[Carolus Linnaeus|L.]]) [[Augustin Pyrame de Candolle|DC.]] }} The '''map lichen''' is a [[species]] of [[lichen]], '''''Rhizocarpon geographicum'''''. It grows on rocks in areas of low [[air pollution]]. Each lichen is a flat patch bordered by a black line of [[spores]]. These patches grow next to each other. This makes the lichen look like a map or a patchwork field. Map lichen is a lichen widely used by climatologists to determine the relative age of deposits. As an example, they might use it in a [[moraine]] systems, to tell how long a rock has been exposed. With this they can also tell about [[glacier|glacial]] advances. The process is called [[lichenometry]]. Lichenometry is based on the assumption that the largest lichen growing on a rock is the oldest individual. If the growth rate is known, the maximum lichen size will give a minimum age for when this rock was deposited. Growth rates for different areas and species can be obtained by measuring maximum lichen sizes on substrates of known age, such as [[gravestone]]s, historic or [[prehistoric]] rock buildings, or moraines of known age (e.g. those deposited during the [[Little Ice Age]]). {{biology-stub}} [[Category:Fungi]]