Yellow map lichen grows on exposed rock surfaces, especially acidic rocks like granite. In Finland, it’s widespread on rocky outcrops and cliffs - especially in SW Archipelago. Yellow map lichen forms patches with distinct black outlines, creating a pattern that resembles a geographic map, hence the name. It´s extremely slow-growing. The age of yellow map lichen is determined using a scientific method called lichenometry. This technique estimates the age of exposed rock surfaces (e.g., moraines, rockfalls, glacial retreats) based on the size of slow-growing crustose lichens, like Rhizocarpon geographicum. Scientists measure the diameter of the largest yellow map lichen. The assumption is that the largest lichen started growing soon after the surface was exposed. The formula is: age = diameter ÷ growth rate. If a lichen is 50 mm wide and grows 0.5 mm/year, it´s age is approximetely 100 years. The larger map lichen in the center of the image is 200–300 years old.
Yellow map lichen grows on exposed rock surfaces, especially acidic rocks like granite. In Finland, it’s widespread on rocky outcrops and cliffs - especially in SW Archipelago. Yellow map lichen forms patches with distinct black outlines, creating a pattern that resembles a geographic map, hence the name. It´s extremely slow-growing. The age of yellow map lichen is determined using a scientific method called lichenometry. This technique estimates the age of exposed rock surfaces (e.g., moraines, rockfalls, glacial retreats) based on the size of slow-growing crustose lichens, like Rhizocarpon geographicum. Scientists measure the diameter of the largest yellow map lichen. The assumption is that the largest lichen started growing soon after the surface was exposed. The formula is: age = diameter ÷ growth rate. If a lichen is 50 mm wide and grows 0.5 mm/year, it´s age is approximetely 100 years. The larger map lichen in the center of the image is 200–300 years old.
