Internal structure of a lichen. Leafy lichens: description, characteristics, structure and features. The ecological role of lichens

Lichen is a living organism formed by the symbiosis of a fungus and algae. Algae can be green algae or blue-green algae. Blue-green algae are actually bacteria, they are called cyanobacteria. So lichen can be a symbiosis of 1) fungus and algae, or 2) fungus, algae and cyanobacteria, or 3) fungus and cyanobacteria.

Quantity different types lichens is about 25 thousand species. Lichens are found on all continents of the Earth, even in Antarctica.

Lichens are ubiquitous, and people have used them since ancient times for various purposes (as food for pets, as medicine and food, for dyeing tissues). However, people did not know for a long time what kind of organism it was. This became known only in the middle of the 19th century.

The special structure of lichens does not make it possible to unambiguously define them to any one kingdom of the living world. They can be attributed to both the plant kingdom and the mushroom kingdom.

Lichens grow very slowly, but they live for a very long time. A lichen can live for hundreds or even thousands of years.

The lichen body is a thallus. In different types of lichens, the thallus is different, it differs in shape and structure, color, size. Most lichens have a thallus of a few centimeters, but there are lichens about a meter long.

There are three types of lichens, depending on appearance thalli: scale, leafy and bushy. Crusty lichens are like a crust adhered to a surface, usually a rock or stone. The leafy lichen has a plate-like thallus. The foliose lichen thallus is attached to the surface by a thick short stalk. A bushy lichen looks like a bush. The bush can rise above the surface or hang.

Bushy lichen

Scale lichen

Lichens come in white, green, yellow, blue, gray and other colors.

Lichens of different colors

The symbiosis of fungus and algae in the body of a lichen is very close, which as a result gives a single organism. The fungal hyphae are intertwined in the thallus, cells of green algae or cyanobacteria are located between them. These cells can be located either singly or in groups.

Lichen structure on the example of Sticta fuliginosa: a - cortical layer, b - gonidial layer, c - core, d - lower cortex, e - rhizines

Thus, lichen combines two very different organisms. The fungus feeds heterotrophically (absorbs ready-made organic substances), and the algae - autotrophically (synthesizes organic substances from inorganic ones). An analogy can be drawn. Mycorrhiza is a symbiosis between higher plants and fungi, and lichen is a symbiosis between lower plants and fungi. However, in a lichen, symbiosis is much closer. After all, the species of fungi that are part of lichens cannot exist without algae at all. Although most of the algae are lichens naturally occurring separately.

The fungal hyphae absorb water with dissolved minerals, and algae or cyanobacteria carry out photosynthesis and form organic matter.

Lichens reproduce by patches of thallus and spores.

The symbiosis of algae and fungus allows a lichen to live in a variety of environmental conditions that are not adapted for life. Lichens are able to grow on rocks, house walls, in the desert and tundra. And, of course, they are ubiquitous in forests. However, lichens are very sensitive to pollution. If the air is smoky, harmful gases are present in it, then lichens die. Therefore, lichens can serve as indicators of the cleanliness of the environment.

Lichens are the first to inhabit rocky ground. Subsequently, they participate in the destruction of rocks, dissolving the substrate. Dying off, lichens participate in the formation of soil, along with other organisms.

Yagel is a lichen that serves as food for reindeer. Some types of lichens are edible for humans, others have antimicrobial properties and are used in medicine.

Nature is rich and extremely diverse, as can be seen by visiting various parts of our vast country or ordering tours to other states. A special group of plants looks curious, which differs from those plants that we are used to seeing every day - lichens. This is both a widespread species, and at the same time its representatives cannot be called ubiquitous. So, let's figure out where lichens grow.

Where does the lichen grow?

Lichens are a group of living organisms that represent an association of fungi with algae that live as a single organism. In nature, there are at least 26 thousand of their species, among which the following are distinguished:

epilithic, growing on rocky surfaces;
epigeic, their habitat is soil (such as);
epiphytic, covering tree trunks.

Moreover, lichens can be found everywhere in the wild - they grow on every continent, not excluding Antarctica. Surprisingly, even in the barren lands of the arctic expanses, this unique species can be found. This is exactly where black lichens grow. There are low temperatures, there is practically no water, but such a dark color helps the body to quickly absorb the solar radiation released in a low amount. Well, black lichen takes water from the snow melting in the sun. For a long time, lichens remained a mystery to scientists. In truth, there is still no single point of view in the scientific world that there is a lichen - a representative of the kingdom of mushrooms or the kingdom of plants.

The growing area where bushy lichens grow is, first of all, bare rocks, trees and soil. Moreover, the lichen feels great in the harsh conditions of the North, in the taiga, highlands, and in the middle of the hot territories of tropical countries. An unpretentious culture, lichen settles high in the mountains and in poor lands. At the same time, lichens, over time, destroying the upper layer of stony soil, when they die off, they leave a humus layer, on which other plants later develop. By the way, lichens grow extremely slowly, for example, the growth of lichen is only 2-3 mm per year.

At the same time, large settlements, especially with a developed industry, cannot be called with certainty the lichen habitat. The reasons why lichens do not grow in cities are quite understandable. The air in cities is polluted, which makes lichen an unacceptable condition. The fact is, for most representatives of lichens, conditions of high oxygen content in the air are important. But this does not mean that lichens cannot be found at all in the urban area. They do not grow in industrial zones, and on the outskirts you can find tree trunks covered with thalli of this biological species.

What lichens grow in Russia?

On a huge territory Russian Federation the most different types lichens. In the spruce forests, gray covers of the bearded lichen can be found descending into the branches. When visiting a pine forest, whole colonies are often found in the form of patterned bedspreads crunching underfoot on a land of white, gray and even pink bushy lichens. We mentioned earlier about one more type of fruticose lichens - this is reindeer moss, better known as "deer moss". In the harsh conditions of the tundra, the deer living there feed on this particular fungus alga.

Sometimes, on stones in almost any region of the country, you can find as if frozen gray-brown foam. It is formed by the so-called crusty lichens.

In nature, leafy lichens are also found (for example, wall xanthoria), which forms a bizarre multi-colored pattern of plates. They cover not only stones, but also tree trunks and branches.

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Lichens are a symbiosis of a fungus and algae, that is, they cannot be considered a single organism, since its individual parts have different genomes.

Lichen structure

The vegetative body of a lichen is called a thallus.

The fungal hyphae form the base of the thallus, forming the lower bark attached to the substrate, and the superficial crustal layer, determining the shape and color of the lichen.

Seaweed occupying the cavities between the hyphae,form a gonidial layer.

Under the layer of algae, mushroom hyphae are loosely located, large gaps between them are filled with air - this is the core. The core is followed by the lower crust, which is similar in structure to the upper one. Tufts of hyphae (rhizoids) pass through the lower cortex from the core, which attach the lichen to the substrate.

In crustal lichens, there is no lower cortex and the fungal hyphae of the core grow together directly with the substrate.

Rice. Lichen structure

Functions of the cortex:

protective;
support;
attaching (nrhizoids are formed in the lower crustal layer);
gas exchange (through perforations (dead parts of the crustal layer), cracks and breaks in the crustal layer).

Algae Zone Function:

photosynthesis;
accumulation of organic matter.

Core function:

conducting air to the cells of algae;
support function (ysome fruticose lichens).

Lichens mainly form:

mushrooms - ascomycetes and basidiomycetes;
algae are most often green (cyanobacteria are less common).

The essence of symbiosis:

The alga gives the fungus organic substances obtained in the process of photosynthesis.
The fungus, having an extensive mycelium, provides the alga with water and minerals.

Such symbiosis of certain species of fungus and algae is so stable that it is perceived as a certain kind organisms.

Lichen classification

According to the shape of the thallus, lichens are divided into:

scale: attached to the substrate with their entire surface (rhizocarpon);
leafy: attached to the substrate at separate points (parmelia, xanthoria).
In some leafy lichens, the thallus is attached with a short stem. (gomf), located in the central part of the thallus.
bushy: attached at one point and branching (cladonia, reindeer lichen, sleeping).
In bushy radially built lichens, on the periphery of the cross section, there is a bark, under it a gonidial layer, and inside - a core.
Crustose lichens grow on their periphery, and bushy ones - with the ends of "twigs".

Rice. Scale lichen Fig. Leafy lichen

Rice. Bushy lichen

Reproduction of lichens

Lichens have vegetative, sexual and asexual reproduction.

Asexual reproduction:

fragmentation;
media- microscopic glomeruli, consisting of one or more algal cells surrounded by fungal hyphae; are formed inside the thallus, and after maturation they come to the surface and burst, scattering diasporas;
isidia- small, variously shaped outgrowths of the upper surface of the thallus, breaking off during maturation.

In both cases, the composition of the detachable structure includes both the fungal and algal components.

Sexual reproduction:

the formation of fruit bodies of various shapes, where spores of sexual reproduction ripen. The development and maturation of the fruiting body can last up to 10 years, and then, over a number of years, the fruiting body is capable of producing spores. A lot of disputes are formed, but not all of them germinate. For germination, conditions are needed, first of all, certain temperature and humidity.

Features of the ecology of lichens

Lichens are characterized by very slow growth:from fractions of a millimeter to several centimeters per year.Most likely, this is due to the small relative volume of autotrophic algae synthesizing organic matter.

Lichens of tropical forests have the highest growth rate, the lowest - the inhabitants of rocks and tundra.

The low growth rate leads to the fact that lichens mainly grow in places where they do not meet with competition from plants.First of all, these are mountainous areas, where they are pioneers on stones and rocks, creating primary soils.Lichens also do not meet competitors in the tundra, where, due to frozen soils, plant roots cannot develop.Lichens often grow as epiphytes in tree crowns.

The fungus's ability to absorb and retain water allows lichens to survive in extremely dry conditions. They can absorb water not only during rains, but also from fog and air saturated with water vapor.

It is interesting that the age of the thallus is often several hundred and thousands of years old.

The meaning of lichens

the formation of primary soils in primary biogeocenoses;
main producersin tundra communities.

Human use of lichens:

lichens are fodder for tundra reindeer husbandry;
some types of lichens are used for food;
are a raw material for the production of dyes (for example, litmus);
applied in folk medicine(for example, falling asleep);
are used in environmental monitoring due to their high sensitivity to chemical pollutants.

Lichens are a group of living organisms.

Their body is folded with the help of a combination of two microorganisms, which are in a symbiotic relationship: a fungus (mycobiont) and an alga (phycobiont or cyanobacteria).

general characteristics

The study of this species is the science of lichenology, which is a department of botany.

For a long time, lichens have been a mystery to scientists, although their use was widespread throughout various branches of human life. And only in 1867 the structure of this species was scientifically proven. Scientists-lichenologists were engaged in this.

At the moment, scientists have discovered more than 25 thousand species, but they all have a similar external and internal structure. The characteristics by which each species should be distinguished are based on structural features.

What does a lichen look like?

As already mentioned, the main part of the species is the body, which is distinguished by a variety of shapes and colors. In this case, the growth can be a plate, a crust that looks like a leaf, in the form of a bush, tube or ball.

The height of the plant also varies within a fairly large range: from 3 centimeters to the height of a person.

Types and names of lichens

Lichenology has divided lichens into several groups due to the shape of the thallus:

In addition, based on the place where they grow, there are:

epigeic (mainly on a land basis);
epiphytic (on a woody base);
epilithic (on stone).

Features of the internal structure

It is possible to see the structure of the lichen under a magnifying device. Lichen is an organism consisting of a part of the fungus - mycelium and algae, intertwined with each other.

Depending on how the cells of algae and fungi are distributed among themselves, another classification is distinguished:

homeomeric, in which the phycobiont is located chaotically among the cells of the mycobiont;
heteromeric, in which there is a clear division into layers.

Lichens with a layered structure are ubiquitous and have the following layer structure:

The cortical layer is composed of mycobiont cells and protects from external influences, especially from drying out.
Superficial or gonidial: contains cells exclusively of phycobiont.
The core consists of a fungus, serves as a skeleton, and also helps to retain water.
The lower cortex serves as an attachment to the base.

Its useful to note: in some species, some types of layers may be absent or have a modified structure.

Where dwell

Lichens are distinguished by their ability to adapt to absolutely any conditions of existence. For example, they grow on bare stones, rocks, walls and roofs of buildings, tree bark, etc.

This is due to the mutually beneficial cooperation of the mycobionts and phycobionts. The vital activity of one complements the existence of the other, and vice versa.

How lichens eat

The implementation of nutrition occurs at the expense of symbiotes. Since fungi do not have the function of autotrophic nutrition, during which the process of converting organic components from inorganic ones takes place, algae supply the body with the necessary elements.

This happens through photosynthesis. And the mushroom supplies the lichen with mineral salts, which it picks up from the incoming liquid. In this way, the process of symbiosis takes place.

How do they reproduce

They reproduce in two ways:

Sexual - is carried out due to sporulation.
Vegetative - for this there are media (algae cell, braided with a thread of mycelium, which is carried by the wind) and isidia (outgrowths that form the surface layer of the thallus).

The value of lichens in nature and human life

Have the following positive effects:

Lichens are famous for their lifespan, because only the growth period can reach 4 thousand years.

As a result, according to them, you can approximately determine the age of the rock.

They are popularly used as fertilizer in the agricultural industry. In addition, their use began in ancient times. Lichens were used as natural dyes.

Lichens are a unique species that carries a lot of useful properties and qualities applicable in virtually any area of human life.

After reading this article, you will learn what the lichen consists of, what forms of these plants are found, and also what role they play in nature and in the economic activities of people. We will also talk about how they absorb moisture, describe their metabolism.

Where do lichens grow?

Lichens are adapted to life even in the most severe conditions, they often fix themselves where other living organisms cannot exist. They go north and south further than other plants. In the Himalayas, they were found at altitudes of more than 5600 m.

Lichens, examples of which are numerous, can exist on almost any surface, be it a sun-scorched rock, a waterless desert, the back of a beetle, or the bleached bone of a dead animal. One species (Verrucaria serpuloides) lives long-term immersion in the icy waters of Antarctica, the other (Lecanora esculenta) is carried by the wind. And although in general lichens are very sensitive to all kinds of industrial waste, such a species as Lecanora conizaeoides thrives noticeably in rather polluted places.

Lichen forms

In accordance with the characteristics of growth, all known species of these plants (and there are 15,000 of them) are divided into three main groups. Let's briefly describe each of them.

Leafy ones thrive in areas characterized by heavy rainfall. As you probably already guessed, they are named so because they resemble leaves in shape. One of their types is shown in the photo below.

The next group is scale (crustal). They are drought tolerant and therefore prevail in deserts. adhere tightly to the substrate on which they grow. Caloplaca heppiana, for example, is often found on walls and gravestones. This and a number of similar plant species of interest to us are used as indicators of the age of the substrate. Lichens of this group are often brightly colored, and the fungus is pigmented.

And finally, bushy are able to take moisture from the air and are found mainly in humid climates. The sizes and appearance of the plants of interest to us are very diverse. Some of them form threads 2.75 m or more, while others are no larger than a pinhead.

What is a lichen made of?

These organisms are formed from plants belonging to two different divisions: algae and fungus. Let's talk in more detail about what a lichen consists of. He is one of the most successful examples of mutualism. This term denotes a mutually beneficial partnership that can be established between two dissimilar organisms.

The algal component is an essential element of what a lichen consists of. These are usually either green or blue-green algae. The fungal component is a representative or ascomycetes. With rare exceptions, lichens include only those plants that consist of one type of fungus and one type of algae. Of the latter, the unicellular green alga Trebouxia is most often included in the composition of these plants (in more than 50% of species), but there may be others.

So, lichens include organisms consisting of a fungus and algae, which are in mutually beneficial cohabitation. Let's give one more example. Xanthoria parietina (pictured below) is commonly found on cliffs along the seaside and on walls and rooftops. Its orange saucer fruiting bodies (apothecia) are almost indistinguishable in structure from the fruiting body of an isolated fungus.

On a cut of a lichen, a thin top layer of tightly intertwined fungal hyphae can be seen. It includes individual cells of green algae. Basically, a lichen is an organism whose body consists of loosely intertwined fungal hyphae, below which there is another thin layer of hyphae, similar to the upper one.

Lichen growth

They grow very slowly. Most scale species rarely increase in size by more than 1 mm per year. Other forms of lichens grow a little faster, but they also add no more than 1 cm per year. Hence it follows that the large species of these plants are of a very respectable age; believe that some representatives of some arctic species are older than 4000 years.

With the help of so-called lichenometry, that is, measurements of lichens, even determine the age of the surface of the rocks. This method was used to establish the age of glaciers, as well as giant megaliths (large boulders). The latter were found on Easter Island in the Pacific Ocean.

The considerable age of these plants shows that they have a fairly high organization and that the relationship between the alga and the fungus is well balanced. But the true nature of this relationship is not yet entirely clear.

Metabolism

Photosynthetic algae, like other green plants, provide food for both partners, since the fungus does not have chlorophyll. Simple carbohydrates synthesized by algae are secreted by it and absorbed by the fungus, where they are converted into other carbohydrates. This metabolism of carbohydrates is at the heart of the symbiotic relationship that led to the formation of lichen. The transition of nutrients from algae to fungus occurs very quickly: it was found that fungi have time to convert sugars from algae within three minutes from the moment photosynthesis begins.

Moisture absorption

Lichens, absorbing a lot of moisture, change significantly in volume. Their height increases significantly. The division of organs that give and absorb moisture is absent in these plants. The bark serves both of these functions. Lichens also lack adaptations to protect them from transpiration, which are well developed, for example, in vascular plants. Most organisms of interest to us receive moisture from the air, and not from the soil. They absorb water vapor. Only some species that attach to the substrate have the ability to take some of the moisture from it.

Use of lichens

Lichens in nature find a variety of uses: they serve as food for animals (for example, they make up two-thirds of the diet of reindeer), are used by birds as material for nests, and serve as a refuge for many species of small invertebrates such as ticks, beetles, butterflies and snails. They also bring benefits to humans. Lichen extracts were once used for dyeing fabrics from which they sewed Yellow, brown, red and purple were obtained from them
paints. Intermediate colors were obtained by additional staining.

(Cetraria islandica) has been used as a cough suppressant for over two centuries. The usnic acid present in some lichens is used by humans to treat superficial wounds and tuberculosis.

Modern research has found antibiotics in them that are effective against diseases such as pneumonia and scarlet fever. In addition, these plants are also used in industry. Thus, from the lichen Roccella sp. a special litmus is obtained - a chemical indicator that turns red in acidic environment and blue in alkaline.