Sun beats down on it constantly. Rhizocarpon geographicum looks like puzzle. Body is thin, crusty layer growing on surface of rock. Forming cracked, irregular pattern. Colour pale grey to yellowish-green. Dark black lines separating patches. Patches look like countries on map. Black lines like borders or rivers. Lichen of ancient map. Looks like chart nobody can read. Makes rock look like world waiting to be explored. What makes it special is pattern. Map lichen is crustose lichen. Meaning it grows flat on rock. Like crust of paint. Rather than upright or leafy. Body divided into small, irregular patches called areoles. Areoles separated by dark black lines called cracks. Pattern looks exactly like map. Patchwork of countries, islands, and continents. Lichen of geography lesson. Turns rock into world. Invites you to trace borders with finger. Map lichen grows very slowly. Few millimetres per year. Large patch may be centuries old. Scientists use map lichen to date rocks. Technique called lichenometry. Size of lichen patch tells them how long rock has been exposed. Lichen of timekeeper. Records age of mountain. Has been watching landscape change for hundreds of years. Biologically it is partnership. Fungus and alga living together. Fungus provides structure and protection. Alga provides food through photosynthesis. Map lichen is pioneer species. One of first to colonise bare rock. Can survive extreme conditions. Heat, cold, drought, and intense sunlight. To find map lichen is to find cracked pattern on rock. Pale, crusty, and mapped. Living chart on stone. Run finger over surface. Feel cracks, borders, texture of map. Lichen of ancient map. Looks like chart nobody can read. Proves mountains have their own language. No one told it otherwise.