Map lichen

Description:

The map lichen (Rhizocarpon geographicum) is a crustose lichen, which grows on rocks in mountainous areas of low air pollution. It is a variable lichen, often mosiac-forming. The glossy thallus forms bright yellowish-green to yellow angular areoles. Conspicuous black prothallus. Innate, irregular-shaped black apothecia to 1.5mm diam. Each lichen is a flat patch bordered by a black line of spores. These patches grow adjacent to each other, leading to the appearance of a map or a patchwork field.

Habitat:

Occurs on hard siliceous rocks, also found on roofing slates. Most frequent in upland and coastal areas. It was spotted on a stone and cement bridge in a mediterranean forest, Dehesa de Valdelatas. Camera Model: NIKON D300. Exposure Time: 1/60 sec. f/45 ISO Speed Rating: 200. Focal Length: 90.0 mm. Flash fired

Notes:

Map lichen is a lichen widely used by climatologists in determining the relative age of deposits, e.g. moraine systems, thus revealing evidence of glacial advances. The process is termed 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 gravestones, historic or prehistoric rock buildings, or moraines of known age (e.g. those deposited during the Little Ice Age).