Lichen

n. any of a number of skin diseases (Pathology)

n. plant organism made up of a fungus and an alga which grow together on rocks (tree trunks, walls etc.)

Lichens are symbiotic associations of a fungus (the mycobiont) with a photosynthetic partner (the photobiont also known as the phycobiont) that can produce food for the lichen from sunlight. The photobiont is usually either green algae or cyanobacteria. A few lichens are known to contain yellow-green algae or, in one case, a brown alga. Some lichens contain both green algae and cyanobacteria as photobionts; in these cases, the cyanobacteria symbiont component may specialize in fixing atmospheric nitrogen for metabolic use.
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n. lichen, plant organism made up of a fungus and an alga which grow together on rocks (tree trunks, walls etc.)

n. lichen, any of a number of skin diseases (Pathology)

n. lichen