What is a Lichen? | The British Lichen Society
The fungus benefits from the symbiotic relation because algae or cyanobacteria produce food by photosynthesis, which is utilized by fungus. The symbiotic relationship between algae and fungi is lichen. The fungal component is called mycobiont while the algae component is called phycobiont. Discusses parasitic and mutualistic relationships of fungi. (fungi and plant roots ) and lichen (fungi and either cyanobacteria or green algae).
Such relation in which both the organisms are benefited from one another is called symbiosis. There about genera and 15, species of lichens. They are found worldwide. They usually grow on the barks of trees, dry logs of wood, bare rocks.
They are xerophytes in nature and can withstand a long period of drought. On the basis of fungal components: The fungal partner belongs to Ascomycetes Basidiolichens: The fungal partner belongs to Basidiomycetes Deuterolichens: The fungal partner belongs to deuteromycetes On the basis of Thallus: In this case, the thallus form crust like structure. It closely adheres to the substrate.
They are found on bark or rock. Graphis, Lecanora, Haematomma In this case, thallus has leaf-like lobes. They are fixed from the substrate by hairy rhizoids like structure called rhizines. They are attached only at central points. Parmellia, Collema, Peltigera Their thalli are cylindrical ribbon-like and branched. It is attached only at the base by basal mucilagenous disc. They are commonly called as shrubby lichens.
Two species of Lecanora have been used as food in the barren plains and mountains of Western Asia and Northern Africa. Certain classes of East Siberian inhabitants use lichens as vegetable diet. It is also used for the preparation of chocolates and pastries. It is a food for reindeer and cattle. Species of Cladonia, Citraria, Evernia, Parmelia are used as fodder.
Usnic acid obtained from the Usnea and Cladonia species is used as an antibiotic against Gram-positive bacteria. Peltigera canina, the dog lichen is used as medicine for hydrophobia in ancient days. Lobaria pulmonaria, lungwort are used for the diseases of lungs respiratory diseases and T. Parmelia is useful against epilepsy. Usnea species are good against urinary diseases.
Lichens : Symbiotic Relation Between Algae and Fungi
Xanthoria sp is used in jaundice etc Some lichens possess anticarcinogenic properties. The lungwort lichen is used in tanning, in perfumery.lichens : Symbiotic Association between Algae and Fungi
In fact, it is thought that many early stages of developing lichen spores may survive using such a parasitic or saprophytic strategy. Lastly, there are many lineages of lichen fungi that are parasitic on other lichens — the so-called lichenicolous lichens!
In some cases, non-lichen fungi have evolved from lichenised forms. These can be specialised opportunistic parasites or saprophytes or even symbionts, competing for nutrients with other fungi in the lichen thallus.
The symbiosis may be more complex than this. Recent work by Spribille et al has found yeasts embedded in the cortex of ascomycete macrolichens, and their abundance correlates with previously unexplained variations in phenotype.
There is also convincing evidence for a consistent presence of non-photosynthetic bacteria within the thalli of all lichens, although the role of these bacteria is as yet unknown. Interestingly, a role for non-photosynthetic bacteria was suspected for many years, as the relichenization of separately cultured fungi and algae in the lab was facilitated by the presence of bacteria.
In fact, a legacy of exclusion from accepted mycological research persisted until the s, despite their obvious affinities with non-lichen fungi.
With the advent of molecular biology, the shared history of lichens and non-lichens has been elucidated and acceptedand we now know that the fungi that form lichens have evolved from many only distantly related lineages across the fungal tree of life, uniting them and their non-lichen relatives in the Kingdom Fungi. Lichen fungi are a heterogeneous group; they are similar only ecologically, in that they share the nutritional strategy of gaining carbon from an internal symbiotic photosynthetic partner, the photobiont.
In the study of lichens, the name and classification belongs to the fungal partner, which in most cases is the dominant member of the association, at least in terms of biomass. Lichen fungi have evolved independently several times within the mushroom-forming fungi and relatives the basidiomycetesbut much more commonly, from within the cup fungi the ascomycetes.
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Probably more than ten distinct major lineages of fungi within the ascomycetes are lichenised. Current estimates suggest that one fifth of all known fungi and half of all ascomycetes are lichenised, with about 28, species worldwide.
As with most organisms, lichen fungi are most diverse and least studied in the tropics. For example, the genus Arthonia is comprised of a mix of lichenised and non-lichenised species and includes many which are specialist parasites, only found on one or a few closely-related host lichens. In a single genus, then, we have a case of lichen parasites evolving from lichen fungi!
Other non-lichen fungi arose from lichenised ancestors, such as Stictis and Ostropa. Fungi are classified in part by the type of spore-producing structures they produce, with the cup fungi ascomycetes named for the open, cup-shaped structures which often bear the sexual spores of the fungi.
Not all ascomycetes have these cup-shaped structures, however, and, easily observed morphological characteristics like fruit type cup-like apothecia versus flask-shaped perithecia, for example cannot always be used to assess relationships.
Unfortunately, this means that not all fungi sharing a single characteristic are likely to be related. However, some order can be distilled. The bulk of lichen diversity belongs to the class including the well-known genera Lecanora, Cladonia, Parmelia and Peltigera Lecanoromycetes, or the Lecanora-groupwhere spores are borne mostly in open or cup-shaped fruits apothecia. This group of fungi is very old, estimated to have evolved during the Carboniferous period.
The very first lichens probably date back to before the origin of land plants, when most of the biodiversity of Earth was in the sea. Many Arthonia relatives also have open cup type fruits, but their development is quite different, giving a clue that they are not closely related to the Lecanora-group.
Instead, they are more closely related to other ascomycetes that have flask-shaped spore-bearing structures perithecia. Similarly, for still other lichen groups, morphological similarities have been confirmed by molecular evidence to point to their widely disparate origins in the ascomycete tree of life. For examples of these, students would be advised to visit the tropics, where the members of the Arthonia- Trypethelium- and Pyrenula- groups form conspicuous and sometimes colourful crusts.
In Britain, the smooth barked trees of the western districts are good places to see some of our Arthonia and Pyrenula species.
Symbiosis in lichens - Wikipedia
Students of lichenology will probably not be surprised to read that lichen fungi can be difficult to identify, partly due to the paucity of morphological characters to go on, but also due to the repeated and independent evolution of such characters.
For example, the fruticose habit has evolved repeatedly within the Lecanora-group, but also within the distantly related Arthonia-group. Unrelated fungi repeatedly evolve similar morphologies to succeed under similar conditions, making morphological identification especially difficult in some groups. Lichen Photobionts Fungi are heterotrophic, meaning that, like animals, they require a carbon source to survive.
The lichen fungi share a common ecological strategy of hosting an internal population of photosynthetic cells, from which they obtain their carbon source in the form of simple sugars.