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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Lichen /li·chen/ 1. any of certain plants formed by the mutualistic combination of an alga and a fungus. 2. [more]Lichen - Community and Resources

Noun
1. any of several eruptive skin diseases characterized by hard thick lesions grouped together and resembling lichens growing on rocks
(hypernym) skin disease, disease of the skin, skin disorder, skin problem, skin condition
(hyponym) lichen planus, lichen ruber planus
2. any thallophytic plant of the division Lichenes; occur as crusty patches or bushy growths on tree trunks or rocks or bare ground etc.
(hypernym) fungus
(hyponym) ascolichen
(member-holonym) Lichenes, division Lichenes

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