|lichen (ˈlaɪkən, ˈlɪtʃən)|
|1.||an organism that is formed by the symbiotic association of a fungus and an alga or cyanobacterium and occurs as crusty patches or bushy growths on tree trunks, bare ground, etc. Lichens are now classified as a phylum of fungi (Mycophycophyta)|
|2.||pathol any of various eruptive disorders of the skin|
|[C17: via Latin from Greek leikhēn, from leikhein to lick]|
lichen li·chen (lī'kən)
Any of various skin diseases characterized by patchy eruptions of small, firm papules.
|lichen (lī'kən) Pronunciation Key
The mutualistic symbiotic association of a fungus with an alga or a cyanobacterium, or both. The fungal component of a lichen absorbs water and nutrients from the surroundings and provides a suitable environment for the alga or cyanobacterium. These live protected among the dense fungal hyphae and produce carbohydrates for the fungus by photosynthesis. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. The more familiar lichens grow slowly as crusty patches, but lichens are found in a variety of forms, such as the tall, plantlike reindeer moss. The association between the different organisms in a lichen is so close that lichens are routinely referred to as a single organism, and scientists classify lichens using the name of the fungal component.