Lichen and trees

Lichens are non-parasitic organisms consisting of a symbiotic relationship between a fungus and a green alga or cyanobacterium. The fungus collects water and minerals from the air and substrate and the alga/bacterium contributes photosynthates and other nutrients to the partnership. The lichen itself grows on the surface of the organism or object (trees, rocks, dead wood, grave stones, etc.) without causing any harm or negative effect to its host.