By contrast, fungi do not make their own carbohydrates. Every fungus needs existing organic matter from which to obtain carbon. In a lichen some of the carbohydrate produced by the photobiont is of course used by the photobiont but some is 'harvested' by the mycobiont.
Worldwide, over 20, species are known and over 3, are known from Australia. There has been scientific study of Australian lichens over the past two centuries, though with somewhat erratic progress during the first century and a half since European settlement. Lichens can be found growing in almost all parts of the terrestrial world, from the ice-free polar areas to the tropics, from tropical rainforests to those desert areas free of mobile sand dunes.
While generally terrestrial a few aquatic lichens are known. The surfaces or substrates on which lichens grow vary from the natural such as soil, rock, wood, bone to the man-made bitumen, concrete, glass, canvas, metal - to give just a few examples. Lichens possess structures not formed by either of the partners and produce chemicals usually absent when the fungus or the photobiont are cultivated separately and so lichens are more than a sum of their parts.
In fact, lichens synthesize over substances, many of them not found elsewhere in nature. Though the fungi that form lichens do not occur in nature as independent organisms, a number of the photobionts can be found in free-living forms. It is possible to separately culture the two partners in the laboratory but it is difficult to resynthesize the lichen.
Success has been achieved when the fungus and photobiont are placed under stress e. As well as having important ecological roles lichens have also been used by humans as food, medicine and for the dyeing of cloth.
For example, traditionally lichens were used to produce the colours of Harris tweed. Lichens are classified with the fungi being sometimes referred to as lichenized fungi. The fungi incorporated into lichens are largely ascomycetes, with very few basidiomycetes involved. Though a number of lichen species can be readily identified in the field the precise identification of many lichens demands examination of their macroscopic and microscopic structures such as reproductive structures, spores and cellular features as well as chemical tests.
The usefulness of the chemical tests lies in the fact that the chemical substances are often species specific. Lichens show a variety of growth forms and there are terms used to name these forms. The following are three very commonly seen types:. Fruticose lichens are erect or pendulous and markedly three-dimensional. The genus Usnea right is an example. Crustose lichens are markedly two dimensional and firmly attached to the substrate by their entire lower surfaces, making it impossible to see a crustose lichen's undersurface.
A crustose lichen looks very much like a thin crust on the substrate. The bright orange Caloplaca is an example. Foliose lichens could be thought of as halfway between crustose and fruticose. Though obviously three dimensional they grow in a more-or-less sheet-like form, but often with a lobed appearance.
They are not attached by their entire lower surfaces to their substrates. Indeed, some foliose lichens are just centrally attached to their substrates with the rest loose, so making it possible to see both the lower and upper surfaces very easily.
Xanthoparmelia substrigosa below is an example. Those three growth forms will account for the majority of genera that most people are likely to see. It is also worth mentioning the concept of a squamulose lichen since the genus Cladonia is very widespread and often shows a squamulose growth form. But the species in the genus also produce upright fruticose structures called podetia - sometimes with the appearance of fairly simple stalks, sometimes flared at the apex and so presenting a somewhat trumpet-like form.
In this photo you can see a Cladonia colony growing on soil. There are numerous squamules on the soil but you can also see a number of the upright podetia with broader apices. Moreover, at the margins of some of the broader apices you can see additional podetia developing.
Here is a closer view, showing an enlargement of part of the previous photo. You can also see that the podetia themselves also have flake-like squamules. Cladonia is not the only squamulose lichen genus, just a very commonly seen one. A colony of a squamulose lichen looks like a scattering of small flakes or scales on the substrate.
A byssoid lichen has a somewhat wispy appearance, like cotton-wool teased out to some degree. Leprose lichens have a powdery or granular appearance. You can find combinations of growth forms in some lichens. For example, some species are crustose centrally but somewhat foliose at the margins.
Just in case you're interested, such a lichen is called placodioid or placoid and Placopsis perrugosa is an example. Lichens are classified as fungi and the fungal partners belong to the Ascomycota and Basidiomycota. Lichens can also be grouped into types based on their morphology. There are three major types of lichens, although other types exist as well. Lichens that are tightly attached to the substrate, giving them a crusty appearance, are called crustose lichens.
Those that have leaf-like lobes are foliose lichens ; they may only be attached at one point in the growth form, and they also have a second cortex below the medulla. Finally, fruticose lichens have rounded structures and an overall branched appearance. Figure 2 shows an example of each of the forms of lichens. Figure 2. Examples of the three types of lichens are shown here.
The doctor explains that ringworm is a general term for a condition caused by multiple species. The first step is to take a scraping for examination under the microscope, which the doctor has already done. He explains that he has identified the infection as a fungus, and that the antifungal cream works against the most common fungi associated with ringworm. However, the cream may not work against some species of fungus. If the cream is not working after a couple of weeks, Anthony should come in for another visit, at which time the doctor will take steps to identify the species of the fungus.
Fungi are incapable of photosynthesis because they lack the green pigment chlorophyll. That is to say, fungi cannot harvest light energy from the sun and generate their own nourishment in the form of carbohydrates. Instead, they need to seek out outside sources of food.
They absorb nutrition from organic substances, that is, carbon containing compounds such as carbohydrates, fats, or proteins. On the other hand, algae and cyanobacteria can conduct photosynthesis, similar to plants. In fact, chloroplasts, which are the site of photosynthesis in land plants, are adapted forms of cyanobacteria.
These early cyanobacteria were engulfed by primitive plants cells sometime in the late Proterozoic, or in the early Cambrian period , according to the University of California Museum of Paleontology. So when a fungus, which is the dominant partner in this relationship, associates with an alga usually from the green algae or cyanobacterium to form a lichen, it is providing itself with constant access to a source of nourishment.
He described it as the controlled growth of a carbon-providing organism, just like we grow wheat, rice or potatoes. He added that cyanobacteria also provide fungi with the additional benefit of nitrogen fixation. This is the biochemical reaction wherein atmospheric nitrogen is converted to ammonia, a more usable form of the element.
In return, algae and cyanobacteria secure a protected environment, especially from damaging ultraviolet rays. Finally, as lichens, fungi, algae and cyanobacteria are able to live in environments that they could not live in otherwise. On his website dedicated to lichen, Alan Silverside, now retired from the University of the West of Scotland, gives the example of the fungus Sticta canariensis. This fungus is capable of forming two different lichen associations with an alga and cyanobacterium, yet both lichens are referred to as Sticta canariensis.
The fungal partner in the lichen symbiosis provides a home for its algal associate to live that is relatively safe from predators and somewhat climate-controlled the algae get exposed to sunlight, but are protected from drying out. Being photosynthetic, the algae provide food for themselves and the fungus.
The algal partner can usually live outside of the lichen in streams, ponds, or wet soil. The fungal partner, however, has become dependent on the algae for its food and cannot live off of decaying organisms like other fungi. Some scientists think the relationship between lichenized fungi and algae is actually a controlled form of parasitism.
Lichens typically consist of one species of fungus and species of algae. The algal partner may be a species of green algae Chlorophyta or a cyanobacterium Cyanophyta, formerly called blue-green algae. Lichens are named for the fungus species rather than the type of algae in the partnership, since the fungus is the more conspicuous member. Some lichens contain additional microbes and the entire structure might be better considered its own little ecosystem. There are at least 18, species of lichens … but probably lots more!.
With the number of fungi species believed to number over 1. Since many fungi look alike superficially, taxonomists have resorted to genetic analysis to differentiate species. Lichens are not just gray, drab, crusts. Actually, lichens come in a rich variety of colors, ranging from bright yellow, red, and orange to green, black, brown, silver, and gray.
Many lichens are flat and leaf-like "foliose". Some lichens become embedded in the upper surface of a rock or cliff and cannot be removed without breaking off a chunk of their substrate.
The many colors of lichens help protect them from too much sunlight or low temperatures. Colors are a byproduct of the complex chemistry of lichen tissues.
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