lichen

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lichen A type of composite organism, which consists of a fungus (the mycobiont) and an alga or cyanobacterium (the phycobiont) living in symbiotic association. A lichen thallus may be crustlike (crustose), scaly or leafy (foliose), or shrubby (fruticose), according to the species. Lichens are classified on the basis of the fungal partner; most belong to the Ascomycotina. Specialized asexual reproductive structures may be produced. Many lichens are extremely sensitive to atmospheric pollution and have been used as pollution indicators.

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