Mutualistic relationship with lichen

Fungi Symbiosis ( Read ) | Biology | CK Foundation

mutualistic relationship with lichen

Lichens are a mutualism formed between fungi and various groups of algae. The photobiont and its relationship with the phytobiont are the same as in M. When both members of the association benefit, the symbiotic relationship is called . This cross-section of a lichen thallus shows the (a) upper cortex of fungal. There about genera and species of lichens. filaments of a fungus in a mutually beneficial relationship (symbiotic relationship).

The simplest of these is simply to separate a piece of the thallus containing both alga and fungus and send it off by wind or water to develop in a new place. This kind of reproduction is common among lichens and generally effective.

There are more highly developed forms of clonal reproduction, two of which are represented in the photographs above. In the first the lichen has produced soredia. Soredia are small bundles of algae held together by fungal hyphae. They are small enough to be carried by wind yet guarantee the presence of both partners.

The illustration above left shows a young thallus of the foliose lichen Peltigera didactyla.

Lichens : Symbiotic Relation Between Algae and Fungi

In this species the upper surface becomes dotted with soralia, special structures for the production of soredia. In the photograph, the soralia have released granular masses of soredia. The other photograph above is a highly magnified view of isidia, small coral-like branches containing both mutualists that can break off and drift to a new habitat.

The lichen in the picture is Xanthoparmelia conspersa, a common lichen on exposed rock in New Brunswick. Lichen habitats One of the fascinating aspects of lichen biology is the ability of these organisms to occupy habitats that would be totally in inhospitable to other organisms.

Thus we can find them growing on the ground in deserts, on the sides of dry rock, hanging from the branches of trees and and even growing on the backs of turtles. They are nearly as easy to find and study in the middle of winter as during the warmer months.

The first of the three photographs above was taken in Saskatchewan, out in an open prairie. The rock in the forground is the highest point in the immediate area; animals sitting there get a panoramic view of the grassland and all that is taking place there. It is a favourite place for birds, especially birds of prey waiting for a mouse or vole that might be moving through the grass.

The orange lichen is a species of Xanthoria that thrives on nitrogen-rich bird droppings left on the rock. Similar species of Xanthoria, as well as members of the related genus Caloplaca, can be found on our seacoast on rocks frequented by gulls and cormorants. The second of the two pictures above is of White Horse Island, a small island in the Bay of Fundy supporting large colonies of nesting birds.

The white colour of the rock is due to a thick layer of bird droppings; the orange material is a species of Caloplaca. The gravestone at left marks the resting place of Roland ThaxterProfessor at Harvard University and brilliant mycologist, known in particular for his monumental studies on the Laboulbeniales. Beside Roland's grave is that of his brother Karl. Both gravestones have become colonized by lichens and are now difficult to read.

Click on the photograph to get an enlarged version of Roland's gravestone Another interesting thing about our coastal lichens is that some of them are highly tolerant of salt, a substance that is toxic to most fungi, including lichenized ones. The picture at right depicts some coastal rocks on the Bay of Fundy near Saint John. At the bottom of the picture are bunches of brown algae, mostly Fucus vesiculosus and Ascophyllum nodosum, commonly called rockweed.

These rockweeds grow in areas along the shore where they will be immersed in seawater, at least at high tide. At the very top of the rock is a patch of orange, probably Xanthoria parietina.

mutualistic relationship with lichen

In between is a black zone consisting of the custose lichen Hydropunctaria maura. Hydropunctaria maura can grow where it is periodically immersed in seawater but is also able to grow in an area just above that where it receives only splash from waves. This "black zone" occupies an area that often goes for days or even weeks without immersion in seawater but will eventually get splashed.

This is a tough place to live: Just the place for a lichen! The picture at right depicts yet another species of Verrucaria mucosa, a close relative of H.

In fact, it releases its ascospores when it is above the water and thus depends upon being exposed to air.

mutualistic relationship with lichen

However, it does not grow in the upper areas of the tide like H. In the picture V. Beneath this algal layer is a third layer of loosely interwoven fungal hyphae without algal cells.

This layer is called the medulla. Beneath the medulla, the bottom surface resembles the upper surface and is called the lower cortex, again consisting of densely packed fungal hyphae. The lower cortex often bears root-like fungal structures known as rhizines, which serve to attach the thallus to the substrate on which it grows.

Lichens sometimes also contain structures made from fungal metabolites, for example crustose lichens sometimes have a polysaccharide layer in the cortex.

Although each lichen thallus generally appears homogeneous, some evidence seems to suggest that the fungal component may consist of more than one genetic individual of that species. This seems to also be true of the photobiont species involved.

Lichen: Two Living Things In One - Biology for Kids

Reproduction Thalli and apothecia on a foliose lichen Many lichens reproduce asexuallyeither by vegetative reproduction or through the dispersal of diaspores containing algal and fungal cells.

Soredia singular soredium are small groups of algal cells surrounded by fungal filaments that form in structures called soralia, from which the soredia can be dispersed by wind. Another form of diaspore are isidia, elongated outgrowths from the thallus that break off for mechanical dispersal.

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Fruticose lichens in particular can easily fragment. Due to the relative lack of differentiation in the thallus, the line between diaspore formation and vegetative reproduction is often blurred.

Many lichens break up into fragments when they dry, dispersing themselves by wind action, to resume growth when moisture returns. Many lichen fungi appear to reproduce sexually in a manner typical of fungiproducing spores that are presumably the result of sexual fusion and meiosis.

Following dispersal, such fungal spores must meet with a compatible algal partner before a functional lichen can form. This may be a common form of reproduction in basidiolichens, which form fruitbodies resembling their nonlichenized relatives.

Among the ascolichens, spores are produced in spore-producing bodies, the three most common spore body types are the apothecia, perithecia, and the pycnidia. Ecology Crustose and foliose lichens on a wall Lichens are often the first to settle in places lacking soilconstituting the sole vegetation in some extreme environments, such as those found at high mountain elevations and at high latitudes.

Some survive in the tough conditions of deserts, and others on frozen soil of the arctic regions. Recent ESA research shows that lichen can even endure extended exposure to space. Lichens must compete with plants for access to sunlight, but because of their small size and slow growth, they thrive in places where higher plants have difficulty growing.

A major ecophysiological advantage of lichens is that they are poikilohydric poikilo—variable, hydric—relating to watermeaning that though they have little control over the status of their hydration, they can tolerate irregular and extended periods of severe desiccation.

Like some mossesliverwortsfernsand a few "resurrection plants," upon desiccation, lichens enter a metabolic suspension or stasis known as cryptobiosis in which the cells of the lichen symbionts are dehydrated to a degree that halts most biochemical activity. In this cryptobiotic state, lichens can survive wider extremes of temperature, radiation, and drought in the harsh environments they often inhabit.

Lichens do not have roots and do not need to tap continuous reservoirs of water like most higher plants. Thus, they can grow in locations impossible for most plants, such as bare rock, sterile soil or sand, and various artificial structures such as walls, roofs, and monuments.

mutualistic relationship with lichen

Many lichens also grow as epiphytes epi—on the surface, phyte—plant on other plants, particularly on the trunks and branches of trees. When growing on other plants, lichens are not parasites ; they do not consume any part of the plant nor poison it. Some ground-dwelling lichens, such as members of genus Cladina reindeer lichenshowever, produce chemicals which leach into the soil and inhibit the germination of plant seeds and growth of young plants.

Stability that is, longevity of their substratum is a major factor of lichen habitats. Most lichens grow on stable rock surfaces or the bark of old trees, but many others grow on soil and sand.

In these latter cases, lichens are often an important part of soil stabilization; indeed, in some desert ecosystems, vascular higher plant seeds cannot become established except in places where lichen crusts stabilize the sand and help retain water. Pine forest with lichen ground-cover When growing on mineral surfaces, some lichens slowly decompose their substrate by chemically degrading and physically disrupting the minerals, contributing to the process of weathering by which rocks are gradually turned into soil.

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While this contribution to weathering is usually benign, it can cause problems for artificial stone structures. For example, there is an ongoing lichen growth problem on Mount Rushmore National Memorial that requires the employment of mountain-climbing conservators to clean the monument. Lichens may be eaten by some animals, such as reindeerliving in arctic regions.

The larvae of a surprising number of Lepidoptera species feed exclusively on lichens. The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungus, which absorb moisture and nutrients from the environment, and usually provide an anchor to it. 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.

mutualistic relationship with lichen

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.