View source for Lichen symbiosis

'''lichen symbiosis''' (''pl.'' lichen symbioses) – a [[symbiosis]] in which one or several [[mycobiont]]s, most often [[ascomycete]]s, rarely [[basidiomycete]]s, form a network of hyphae that embrace one or several populations of [[photobiont]]s, either [[eukaryotic algae]] or [[cyanobacteria]] or both. Some forms of symbiotic associations are typically not treated as lichen symbioses. For example, the symbiosis formed by the [[zygomycete]] ''Geosiphon pyriforme'' is more accurately referred to as [[endocytobiosis]], i.&nbsp;e., a specialized form of [[endosymbiosis]], where the cyanobacterium cells of the genus ''Nostoc'' inhabit the [[coenocytic]] hyphae. In contrast, photobiont cells of lichens always remain extracellular; though sometimes penetrated by haustorial hyphae, the photobiont cells do never occur within the hyphal cells. Also, the associations of symbiotic fungi growing inside thalli of brown algae (Phaeophyta) are distinctly different from lichen symbioses. These symbioses, where the alga, not the fungus, forms the main structure that is inhabited, are more accurately called [[mycophycobioses]].

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