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[[Image:Haeckel Lichenes.jpg|thumb|230px|"Lichenes" from [[Ernst Haeckel]]'s ''Artforms of Nature'', 1904]]'''Lichens''' are [[symbiosis|symbiotic]] associations of a [[fungus]] (the mycobiont) with a [[Photosynthesis|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. The word is pronounced as though it is spelled "liken" ({{IPA2|laɪkən}}).

[[Image:Haeckel Lichenes.jpg|thumb|230px|"Lichenes" from [[Ernst Haeckel]]'s ''Artforms of Nature'', 1904]]'''Lichens''' are [[symbiosis|symbiotic]] associations of a [[fungus]] (the mycobiont) with a [[Photosynthesis|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 at nitrogen for metabolic use. The word is pronounced as though it is spelled "liken" ({{IPA2|laɪkən}}).

The body (thallus) of most lichens is quite different from that of either the fungus or alga growing separately, and may strikingly resemble simple plants in form and growth (Sanders 2001). The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations; however, the algal cells are never enclosed inside the fungal cells themselves. (The fungus ''[[Geosiphon|Geosiphon pyriforme]]'' is unique in that it encloses a cyanobacterial symbiont inside its cells, but this exceptional association is not usually considered to be a lichen.) The fungus may or may not penetrate into the algal cells with fine [[Hyphae|hyphal protrusions]].

The body (thallus) of most lichens is quite different from that of either the fungus or alga growing separately, and may strikingly resemble simple plants in form and growth (Sanders 2001). The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations; however, the algal cells are never enclosed inside the fungal cells themselves. (The fungus ''[[Geosiphon|Geosiphon pyriforme]]'' is unique in that it encloses a cyanobacterial symbiont inside its cells, but this exceptional association is not usually considered to be a lichen.) The fungus may or may not penetrate into the algal cells with fine [[Hyphae|hyphal protrusions]].