Lichens are a symbiotic representation of mutualism involving a fungus and a cyanobacterium or alga. Within this mutualism, that is, a symbiosis in which both organisms benefit, there exists a photobiont, the cyanobacterium or alga, which contains chlorophyll and photosynthesizes, producing carbohydrates for use by the fungi and itself. Also, there is a mycobiont, the fungus, whose symbiotic roles include the provision of structure and anchorage, protection from dessication, as well as providing the alga with inorganic nutrients and water. Moreover, lichens exhibit several unique features as it relates to their diverse morphology and ecology. With regards to their morphology, lichens have three major forms which are described as crustose (crusty), foliose (leafy) and fruticose (shrubby). Lichen ecology is also of significance in terms of habitat; their importance in nutrient cycling and the preventing erosion; indication of pollution as well as their characteristic ability to colonize areas. Furthermore, these factors all contribute to some of the many uses for which lichens are employed.
Firstly, lichens exhibit many morphological differences, with the three main distinctions being either crustose, foliose or fruticose. More importantly, the main premise for distinguishing morphologies is the thallus shape and structure. The thallus refers to the composite body of the lichen and it is filamentous comprising of hairlike growths called rhizines which anchor the lichen to the substrate. Another factor which constitutes the morphology of lichens is the distribution of the photobiont and mycobiont in the lichen, as well as their growth with respect to the substrate. Another interesting feature of lichens is exemplified in their unique ecology. First of all, lichen growth occurs primarily in terrestrial habitats, with a minority growing aquatically. A wide range of habitats such as forest understoreys, tree leaves and bark, sand deserts and even organisms (e.g....
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