Lichens - organisms that have emerged due to fungi symbiosis with algae or cyanobacteria. The fungus forms the basis of a body lichen and algae cells contained within. Algae capable of photosynthesis and the fungus provides nutrients and protects it from adverse external factors.
Lichens undemanding to living conditions they endure cold, heat and almost completely dry, but strongly affected by pollution. Grow very slowly (often less than a millimeter per year). Some of them live so long that are among the oldest living organisms planet. We know about 20 000 species of lichens.
