Lichens are a peculiar group of perennial plant organisms, the body of which consists of two types of organisms - an autotrophic phycobiont and a heterotrophic mycobiont, forming a single symbiotic organism.

Lichens are complex organisms consisting of fungi and algae, forming, as it were, a new organism, with new morphological, physiological and ecological properties.

Phycobiont is an algae, mainly green algae and less often blue-green or yellow-green.

Most lichen algae are found in a free-living state, but some of their species are known only as part of lichens.

Green lichen algae are represented by the genera Trebonxia, ​​Parmella, Gleocystis, Coccomyces and other microscopic algae. Of the filamentous greens, species of the genera Trentepohlia and Cladophora are most widely distributed in lichens.

Of the blue-greens, Nostoc, Anabaena, Gleocapsa, Hyella, Chroococcus, Stigonema, Calothrix, Dichothrix are often found.

Of the yellow-green (variegated) algae, lichens most often include species from the genus Heterococcus.

In total, 28 species of algae are found in lichens, of which up to 90% are algae from the genera Trebonxia, ​​Nostoc, Trentepohlia.

Mycobiont is a fungus, most often represented by a species of marsupial fungi - pyrenomycetes or discomycetes. Only in some tropical and subtropical lichen species does the fungus belong to the basidiomycetes. A small group of lichens has imperfect fungi with non-cellular mycelium.

The fungi that make up lichens are completely in the air and have a number of features - the walls of the fungal cells are perforated, the cells are connected by cytoplasmic bridges. The hyphal sheaths are thickened and provide mechanical stability to the thallus. In many lichen-forming fungi, hyphae can become mucilaginous, which is not usually the case in free-living fungi. Lichen fungi have fat cells.

Lichens can almost always be distinguished from members of other plant groups.

They differ from algae not in their green color, in a different type of thallus, and in their habitat.

They are well distinguished from mushrooms by the appearance of the thallus and living not in the substrate, but on its surface.

From mosses, with which the higher representatives of lichens are often mixed, they differ in their non-green color and the lack of differentiation into stems and leaves.

Lichens can live where neither fungi nor algae are able to live on their own. At the same time, the fungus provides algae with water and mineral salts, and itself uses organic substances synthesized by algae, which is fully consistent with the symbiotic mode of existence.

As a rule, lichen symbionts are one type of fungus and one type of algae, but some lichens, in addition to one type of fungus, may include two types of algae - green and blue-green.

Lichen, being a symbiotic organism, differs from free-living fungi and algae in its morphological, anatomical, physiological, biochemical, ecological, and qualitative parameters.

The structure, life forms of lichens, arising from the interaction of fungi and algae, are not found separately. Their structure is the result of a long shaping process based on symbiosis. Lichens also produce special substances that are not found in other groups of organisms.

The vegetative body of lichens, called the thallus or thallus, like other lower plants, is not differentiated into leaves, stem and root.

The vegetative body of lichens consists entirely of intertwined fungal hyphae, between which algae are located.

In most lichens, dense plexuses of fungal filaments form the upper and lower cortical layers. Under the upper crustal layer is a layer of algae, where photosynthesis takes place and organic matter accumulates. Below is the core, consisting of loosely located hyphae and air cavities. The function of the core is to conduct air to the algae cells.

The color of the lichen thallus is due to the presence of various pigments and can be gray, gray, greenish, yellow, golden, orange, brown, almost black, light brown, etc.

The shape and size of lichens is different.

Their sizes vary from a few millimeters to several centimeters.

According to the shape of the body and the external structure of the lichen, there are three main morphological types of lichen thalli:

Scale (Graphis scripta), the body of the thallus adheres tightly to the substrate in the form of scales, crusts up to 5 mm thick, granular or dusty deposits. They are found on the bark of trees, on the surface of the soil, on the surface of stones and rocks. By releasing acidic substances, scale lichens cause the destruction of stones.

Leafy (Hypogimnia physodes), the thallus has a rounded shape, often with jagged edges (leaf-like). Their diameter is 10 - 20 mm. Attached to the substrate are bundles of fungal hyphae - rhizidia, covered with a cortical layer. Leafy lichens are characterized by layer differentiation.

Bushy (Cladonia alpestris, Cladonia stellaris), slevishche consists of simple or branched stems and plates, called podetia. They are the most organized lichens. Their thallus is an upright or hanging bush. Hanging (epiphytic) lichens are large in size. For example, a usnea that settles on tree branches in taiga forests can reach 7-8 meters in length.

Lichens are attached to the substrate by special outgrowths located on the underside of the thallus.

The internal structure of lichens is not the same. The most primitive are some scale lichens, in which algae cells are distributed evenly between the filaments of the fungus - hyphae.

The thalli of more highly organized lichens have several layers of cells, each of which performs a specific function.

Anatomically, two types of lichen thalli are distinguished:

The first type is homeomeric, in which the cells of the phycobiont (algae) are evenly distributed in the thickness of the thallus and the hyphae of the fungus are evenly distributed in the mucus secreted by them in all directions;

The second type of lichen thallus is heteromeric, characterized by some differentiation of the thallus. From above, the thallus is covered with an upper bark consisting of tightly woven hyphae of the fungus. Inside the thallus, the hyphae are located loosely and between them there are voids filled with air. These air layers receive carbon dioxide and oxygen necessary for respiration and photosynthesis. From below, the thallus is covered with a lower bark, through which the hyphae of the fungus pass, with the help of which the lichens are attached to the substrate.

The presence of the lower bark of the thallus is inherent in leafy and bushy lichens. Scale lichens do not have a thallus lower bark, because they grow together with the substrate core.

Lichens reproduce in three ways: sexually, asexually and vegetatively. Lichens reproduce by spores that form a fungus, or vegetatively - by breaking off pieces of thalli and then germinating in a new place. Fungal spores can be unicellular or multicellular. Once in favorable conditions, they form the primary mycelium. The further development of this mycelium and the formation of the thallus depend on whether the hyphae of the fungus meet the algae corresponding to this type of lichen. If there are no such algae on the substrate where the primary mycelium grows, the primary mycelium dies, and if there is, then the thallus begins to form.

In terms of chemical composition, lichens, like all other plants, consist of a large amount of proteins, fats, carbohydrates and mineral salts.

The most characteristic distinguishing feature of lichens is their high content of carbohydrates, chemically close to cellulose. Lichenin, isolichenin and evernin were found among polysaccharides.

Lichens are characterized by the presence of a very powerful enzyme apparatus. They have both endoenzymes (amylase, cellulase, lichenase, tannase, lipase, urease, catalase, chymase, peroxidase, asparaginase, oxidase, tyrosinase, phenolase) and exoenzymes (lipase, invertase, amylase, lichenase, tannase, urease, catalase). , zymase, asparaginase, phenolase), which provide lichens with biosynthesis processes and allow them to actively participate in the cycle of substances and be used in biotechnology.

The activity of lichen enzymes is significantly influenced by the geographic zone, substrate and habitat, temperature, radiation, time of day and year, degree of cleanliness of the environment, etc.

Lichen components provide the synthesis of lichen acids, which promote metabolic processes, protect against the harmful effects of solar radiation, and ensure the impermeability of the thallus. Lichen acids contribute to the penetration of oxygen, carbon dioxide and atmospheric nitrogen into the thallus.

The composition of lichens includes a group of substances that are similar in nature to tannins and tannins, but have a simpler structure. These substances are called lichen acids. They can be colorless or have a red, brown, yellow, violet, orange, black color; they are easily soluble in ether and insoluble in water. The color of lichens depends on the color range of lichen acids.

With their acids, lichens have a chemical and physical effect on the substrate.

Lichens are found in all botanical and geographical zones (in temperate and cold regions, in humid and temperate tropics)

Lichens are distributed throughout the globe - from polar cold rocks to hot desert stones. Lichens live in the Arctic and Antarctic, at the edge of eternal snow and in the mountains, in waterless deserts, i.e. where the most difficult conditions for life, due to the fact that they are able to stay in a dry, dehydrated state for a long time, suspending all vital functions until the first moistening. The humidity of the lichen thallus depends on the humidity of the environment. Dry lichens very quickly absorb moisture, the source of which can be rain, fog, dew, melting snow, atmospheric water vapor. It should also be noted here that along with water, lichens absorb various pollutants, and this, in turn, can cause the death of lichens.

The areas of distribution (ranges) of various lichens are different.

Their distribution is due to many factors, of which the main ones are the ability of lichens to withstand the adverse effects of the environment, the range and speed of the transfer of part of the plant used for reproduction, undemanding to the substrate, etc.

The harsh living conditions of lichens cause their slow growth. This is due to the relatively weak ability for photosynthesis, i.e. independent formation of organic substances due to solar energy.

The intensity of the process of photosynthesis (as a source of carbohydrates) in lichens depends on environmental conditions, which include environmental humidity, light, temperature, atmospheric pollution with various pollutants, the presence of nitrogen, mineral salts, etc.

The soil, as a source of nutrients, also plays a significant role in the process of lichen growth. The soil on which lichens grow in most cases is poor in organic matter necessary for nutrition.

Lichens grow slowly and develop slowly, and this was one of the reasons for the displacement of lichens into harsh habitats, but in these places lichens are not threatened by competition from stronger rivals.

In particular, many of them develop on tree trunks, on stones and rocks, on poorly fertile soils, in the tundra, on mountain tops, in pine forests, etc. Settling on barren soils, lichens gradually loosen it and enrich it with organic matter and contribute to the formation of a fertile soil layer.

Lichens grow slowly and develop slowly, but their life expectancy is very long (several tens of years).

Lichens are widely distributed in different ecological systems of the globe. They are an integral part of soil biocenoses, trunks and branches of trees, boulders, rocks and other substrates, where they form groups - synusia. The main condition for the settlement of lichens on a particular substrate is the long-term immobility of the substrate with certain chemical properties. The species composition of lichen synusia and their biomass are much less compared to the groups of flowering and other representatives of higher plants, but this does not in the least detract from their role in the processes of the circulation of substances that ensure the life of our planet.

In relation to substrates and environmental factors, several ecological groups of lichens are distinguished: growing on soil, trees, stones, wood, etc. growing on soil, trees, stones, wood, etc.

Ground (epigean) lichens are lichens that live in places that are not very suitable for higher plants due to a small amount of nutrients. Such places include sandy soils, tundra, semi-desert, peat bogs, forest tundra, as well as places with adverse climatic conditions.

Ground lichens include: Peltigera canina, P.erumpens, P.aphthosa, P.malacea, P.polytactyla, Cetraria islandica. Stereocaulon tomentosum, Cladonia rangiferina, C.sylvatica, C.alpestris, C.deformis, C.mitis, Ochrolechia androgyna, O.tartarea, O.frigida, Alectoria ochruleuca, Cetraria islandica, C.cucullata.

Among the ground lichens there are nomadic ones, in which there is practically no connection with the soil and they are carried from place to place by the wind, and there is also a group of lichens that are permanently attached to the soil.

Nomadic ground lichens include Aspicilia esculenta, Parmelia vagans, Parmelia ryssolea, Carnycularia steppae.

Attached to the soil are Ramalina polymorpha, R. strepsilis, Parmelia pulla. Baeomyces roseus, B.rufus live on clay soil.

The species of the genera Collema and Verrucaria settle on limestones.

On soils that are not suitable for the development of other plants (in the tundra, forest-tundra, in the desert), species of the genera Cladonia, Cladina settle and live. Alectria, Cetraria, Stereocaulon, Ochroleuchina.

Cetraria pinastri, Cladonia digitata, species of the genus Peinigera are found in the forest and light forests.

Epiphytic lichens inhabit trees and shrubs.

They are attached to the bark or surface of the leaves. Their thallus can develop not only on the bark, but also under the bark.

Representatives of epiphytic lichens are: Alectoria alivacea, Bacidia apiahica, Bryopogon implexum, B.chalybeiforme, Cattilaria bouteillei, Evernia prunastri, E.furfuracea, E.thamnodes, Graphys scripta, Lobaria pulmonaria, Parmelia sulcata, P.physodes, Physcia pulverulenta, Ph. hispida, Ph.stellaria, Ph.ciliata, Ramalina thrausta, R.farinacea, R.pollinaria, Usnea longissima, U.dasypoga, U.hirta, U.florida, Xanthoria parientina, as well as species of the genera Cladonia, Cetraria, Hypogymnia.

Episcal lichens develop on treated, bare and decaying wood.

Epiphilic lichens grow on the leaves and needles of evergreen trees.

Epilithic (rock or scale) lichens settle and live on stones and rocks. Among them: Cetraria nivalis, C.fahlunensis, Collema multifidum, Gyrophora hirsuta, Gasparrinia decipiens, Parmelia sulcata, P.omphalodes, P.centrifuga, Rhisocarpon geographycum, Umbilicaria pustulata, as well as species of the genera Biatora, Placopsis, Verrucaria, Lecanora, Physcia, Dermatocarpon, Sphaerophorus, Stereocaulon.

The amphibious (aquatic) lichens living in the aquatic environment, in the zone of splashes, tides, surfs, in places often flooded with water, include: Dermatocarpon miniatum, D.aquaticum, hydrthyria venosa, Lecidea albocoerrulescens, Rhizocarpon obscuratum, etc.

GROUP OF LICHES

OPTION 1

A1. The lichen is

1) plant

2) a colony of bacteria

3) fungus

4) symbiosis of two organisms

A2. The body of a lichen consists of

1) thallus

2) organs

3) single cell

4) modified shoots

AZ. In the composition of lichen, algae plays a role

1) autotroph

2) heterotroph

3) predator

B1.

A. The composition of the lichen includes a cap mushroom.

B. Lichen is an autoheterotrophic organism in terms of nutrition.

1) Only A is true

2) Only B is true

3) Both statements are correct

4) Both judgments are wrong

B2. Choose three true statements. Distinguish the main types of lichen thallus

1) scale

2) grassy

3) woody

4) shrub

5) leafy

6) bushy

BZ. Establish a correspondence between the life process of a fruticose lichen and a component of its thallus.

A. Carry out photosynthesis

B. Absorb ready-made organic substances

B. Form organic substances in the light

D. Absorb water and mineral salts from the soil

THALL COMPONENT

1) Algae cells

2) Mushroom vultures

IN 1.

What are the reasons for the widespread distribution of lichens? Name at least three reasons.

Lichens are able to tolerate prolonged drying. Lichens reproduce mainly vegetatively, their body is very fragile and breaks easily, new bodies grow from broken pieces, and small particles are easily carried by wind and birds over long distances (they also reproduce by spores). Lichens are able to tolerate very low temperatures.

AT 2.

Lichens are a complex organism, including algae and ... (A). Algae obtain organic matter in a process called... (B). Mushrooms supply the entire body with water and ... (B). This type of relationship is called ... (D).

Glossary: ​​1. Symbiosis. 2. Mushroom. 3. Root nutrition. 4. Minerals.

Answer: A-2, B-3, C-4, D-1.

OPTION 2

For each task, choose one correct answer from the four given.

A1. Mutually beneficial cohabitation of fungus and algae forms

1) mycorrhiza

2) lichen

3) mold mycelium

4) the fruiting body of the fungus

A2. In the composition of the lichen, the fungus plays a role

1) autotroph

2) heterotroph

3) predator

AZ. Algae cells in the body of a lichen

1) produce organic matter

3) absorb ready-made organic substances

4) destroy the threads of the mycelium

B1. Are the following statements true?

A. Lichen is an integral living organism, the components of which are interconnected.

B. Lichens grow in all biogeographic zones.

1) Only A is true

2) Only B is true

3) Both statements are correct

4) Both judgments are wrong

B2. Choose three true statements. Lichens breed

1) parts of the thallus

2) disputes

3) seeds

4) shoots

5) sexually

6) budding

BZ. Establish a correspondence between the life process of a lichen and the way it feeds.

LICHEN LIFE PROCESSES

A. Algae cells form carbohydrates

B. The process of photosynthesis proceeds in chloroplasts

B. Absorb ready-made molecules of organic substances

D. Cells absorb minerals with the entire surface

FOOD METHOD

1) Autotrophic

2) Heterotrophic

Write down the corresponding numbers in the table.

IN 1. Task with a detailed free answer (several elements).

Specify the importance of lichens in nature. Name at least three values.

They prepare the soil for other organisms, are animal feed (moss reindeer moss), and are an indicator of air purity.

AT 2. Read the text. Fill in the gaps with the numbers that represent the words from the dictionary.

The group of cap mushrooms includes champignon, boletus, ... (A). A perennial mycelium on the soil surface forms ... (B) and consists of ... (C). The nutrition of the fungus occurs as a result of ... (D).

Glossary: ​​1. Fruiting body. 2. Nutrient absorption. 3. Legs and hats. 4. Fly agaric.

Answer: A-4, B-1, C-3, D-1.

Biology test Group lichens for 7th grade students. The test includes 2 options, each option consists of 3 parts (part A, part B and part C). Part A has 3 questions, Part B has 3 questions, and Part C has 2 questions.

Tasks A - basic level of difficulty
Tasks B - advanced level of difficulty
Tasks B - high level of complexity

1 option

A1. The lichen is

1) plant
2) a colony of bacteria
3) fungus
4) symbiosis of two organisms

A2. The body of a lichen consists of

1) thallus
2) bodies
3) single cell
4) modified shoots

A3. In the composition of lichen, algae plays a role

1) autotroph
2) heterotroph
3) predator
4) victims

B1.

A. The composition of the lichen includes a cap mushroom.
B. Lichen is an autoheterotrophic organism in terms of its mode of nutrition.

1) Only A is true
2) Only B is true
3) Both statements are correct
4) Both judgments are wrong

B2. Choose three true statements. Distinguish the main types of lichen thallus

1) scale
2) grassy
3) woody
4) shrub
5) leafy
6) bushy

B3. Establish a correspondence between the life process of a lichen and a component of its thallus.

A. Carry out photosynthesis
B. Absorb ready-made organic substances
B. Form organic substances in the light
D. Absorb water and mineral salts from the soil

Thallus component

1. Algae cells
2. Fungal hyphae

IN 1.

What are the reasons for the widespread distribution of lichens? Name at least three reasons.

AT 2. Read the text. Fill in the gaps with the numbers that represent the words from the dictionary.

Lichens are a complex organism that includes algae and ... (A). Algae obtain organic matter in a process called ... (B). Mushrooms supply the entire body with water and ... (B). This type of relationship is called ... (D).

Glossary:
1. Symbiosis.
2. Mushroom.
3. Root nutrition.
4. Minerals.

Option 2

A1. Mutually beneficial cohabitation of fungus and algae forms

1) mycorrhiza
2) lichen
3) mold mycelium
4) the fruiting body of the fungus

A2. In the composition of the lichen, the fungus plays a role

1) autotroph
2) heterotroph
3) predator
4) victims

A3. Algae cells in the body of a lichen

B1. Are the following statements true?

A. Lichen is an integral living organism, the components of which are interconnected.
B. Lichens grow in all biogeographic zones.

1) Only A is true
2) Only B is true
3) Both statements are correct
4) Both judgments are wrong

B2. Choose three true statements. Lichens breed

1) parts of the thallus
2) disputes
3) seeds
4) shoots
5) sexually
6) budding

B3. Establish a correspondence between the life process of a lichen and the way it feeds.

Life processes of lichens

A. Algae cells form carbohydrates
B. The process of photosynthesis proceeds in chloroplasts
B. Absorb ready-made molecules of organic substances
D. Cells absorb minerals with the entire surface

Feeding method

1. Autotrophic
2. Heterotrophic

IN 1. Task with a detailed free answer (several elements).

Specify the importance of lichens in nature. Name at least three values.

AT 2. Read the text. Fill in the gaps with the numbers that represent the words from the dictionary.

The group of hat mushrooms includes champignon, boletus, ... (A). Perennial mycelium on the soil surface forms ... (B) and consists of ... (B). The nutrition of the fungus occurs as a result of ... (D).

Glossary:
1. Fruiting body.
2. Nutrient absorption.
3. Legs and hats.
4. Fly agaric. ­

Answers to the biology test Group lichens
1 option
A1. 4
A2. 1
A3. 1
B1. 2
B2. 156
B3. 1212
IN 1. Ease of vegetative propagation. 2. Able to survive prolonged drying. 3. Transfer of parts of the thallus by wind over long distances.
AT 2. 2341
Option 2
A1. 2
A2. 2
A3. 1
B1. 3
B2. 125
B3. 1122
IN 1. 1. Algae in the body of a lichen use solar energy to form organic matter. 2. Threads of mycelium decompose organic matter to mineral salts. 3. Form the soil layer.
AT 2. 4132

Lichens can be found almost everywhere, even in Antarctica. This group of living organisms has been a mystery to scientists for a long time, even now there is no consensus about their systematic position. Some believe that they should be attributed to the plant kingdom, while others - fungi. Next, we consider the types of lichens, the features of their structure, their significance in nature and for humans.

General characteristics of lichens

Lichens are the lowest group of organisms that consist of a fungus and algae that are in symbiosis with each other. The first are most often representatives of phycomycetes, ascomycetes or basidiomycetes, and the second organism is green or blue-green algae. Between these two representatives of the living world there is a mutually beneficial cohabitation.

Lichens, regardless of variety, do not have a green color, most often they can be gray, brown, yellow, orange or even black. It depends on the pigments and also on the color of the lichen acids.

Distinctive features of lichens

This interesting group of organisms is distinguished by the following features:

• The cohabitation of two organisms in a lichen is not accidental, it is due to historical development.
• Unlike plants or animals, this organism has a specific external and internal structure.
• The physiological processes occurring in the fungus and algae differ significantly from those in free-living organisms.
• Biochemical processes also have their own distinctive features: as a result of vital activity, secondary metabolic products are formed that are not characteristic of any group of living organisms.
• Special way of reproduction.
• Attitude to environmental factors.

All these features baffle scientists and do not allow to determine the permanent systematic position.

Lichen varieties

This group of organisms is often called the "pioneers" of land, since they can settle in completely lifeless places. There are three types of lichens:

1. Scale lichens. They got their name for the shape, similar to scale.
2. Leafy lichens. They look like one large leaf blade, hence the name.
3. fruticose lichens resemble a small bush.

Consider the features of each type in more detail.

Description of scale lichens

Almost 80% of all lichens are scale. In their form, they look like a crust or a thin film, firmly fused with the substrate. Depending on the habitat, scale lichens are divided into:

Due to their distinctive appearance, this group of lichens can be completely invisible and blend in with their surroundings. The structure of scale lichens is peculiar, so they are easy to distinguish from other species. But the internal structure is almost the same for everyone, but more on that later.

Territories of scale lichens

We have already considered why scale lichens got their name, but the question arises: are the habitats different? The answer can be given in the negative, because they can be found in almost every latitude. These organisms are amazingly able to adapt to absolutely any conditions.

Scale types of lichens are distributed throughout the planet. Depending on the substrate, one or another species predominates. For example, in the Arctic it is impossible to meet species that are common in the taiga, and vice versa. There is a binding to a certain type of soil: some lichens prefer clay, while others feel calm on bare rocks.

But among the wide variety of this group of organisms, you can find species that live almost everywhere.

Features of leafy lichens

The thallus of this species has the form of scales or plates of medium size, attached to the substrate with a bundle of fungal hyphae. The simplest thallus resembles a rounded leaf blade, which can reach a size of 10-20 cm in diameter. With this structure, the thallus is called monophilic. If there are several plates, then polyphilic.

A distinctive feature of this type of lichen is the difference in the structure and color of the lower and upper parts. There are nomadic forms.

"Bearded" lichens

This name was given to fruticose lichens for their thallus, consisting of branched filaments that grow together with the substrate and grow in different directions. The thallus resembles a hanging bush, there are also upright forms.

The sizes of the smallest representatives do not exceed a few millimeters, and the largest specimens reach 30-50 cm. In tundra conditions, lichens can develop attachment organs, with the help of which organisms protect themselves from separation from the substrate in strong winds.

The internal structure of lichens

Almost all types of lichens have the same internal structure. Anatomically, there are two types:

It should be noted that those lichens that belong to scale do not have a lower layer, and the hyphae of the core directly grow together with the substrate.

Nutritional features of lichens

In the process of nutrition, both organisms living in symbiosis take part. Fungal hyphae actively absorb water and minerals dissolved in it, and algae cells have chloroplasts, which means they synthesize organic substances as a result of photosynthesis.

We can say that hyphae play the role of the root system, extracting moisture, and algae act as leaves. Since for the most part lichens settle on lifeless substrates, they absorb moisture with their entire surface; not only rainwater, but also fog and dew are suitable for these purposes.

For normal growth and vital activity, lichens, like plants, need nitrogen. If green algae are present as a phycobiont, then nitrogen compounds are extracted from solutions when the thallus is saturated with moisture. It is easier for lichens, which have blue-green algae, they are able to extract nitrogen from the air.

Lichen reproduction

Regardless of the variety, all lichens reproduce in the following ways:

Considering that these organisms grow very slowly, we can conclude that the process of reproduction is also quite long.

Ecological role of lichens

The significance of this group of organisms on the planet is quite large. They are directly involved in the process of soil formation. They are the very first to settle in lifeless places and enrich them for the growth of other species.

Lichens do not require a special substrate for life, they can cover a barren area, preparing it for plant life. This is due to the fact that in the process of life, lichens secrete special acids that contribute to the weathering of rocks, oxygen enrichment.

Settling on bare rocks, they feel absolutely comfortable there, gradually creating favorable conditions for other species. Some small animals are able to change their color to match the color of lichens, thus disguise themselves and use them to protect themselves from predators.

The value of lichens in the biosphere

Currently, more than 26 thousand species of lichens are known. They are distributed almost everywhere, but it is surprising that they can serve as an indicator of the purity of the air.

These organisms are quite sensitive to pollution, therefore, in large cities near roads, lichen plants are practically not found. They simply do not survive there and die. It should be noted that scale lichens are the most resistant to poor environmental conditions.

Lichens are also directly involved in the circulation of substances in the biosphere. Since they belong to autoheterotrophic organisms, they easily accumulate the energy of sunlight and create organic substances. Participate in the process of decomposition of organic matter.

Together with bacteria, fungi and algae, lichens create favorable conditions for higher plants and animals. Settling on trees, these symbiotic organisms cause practically no harm, since they do not penetrate deep into living tissues. In some ways, they can even be called defenders, because a plant covered with lichens is less attacked by pathogenic fungi, lichen acids inhibit the growth of wood-destroying fungi.

But there is a downside: if the lichens grow too much and cover almost the entire tree, then they close the lentils, disrupting gas exchange. And for insect pests, this is a great refuge. For this reason, it is better to control the growth of lichens on fruit trees and clean the wood.

The role of lichens for humans

The question of the role of lichens in human life cannot be omitted. There are several areas where they are widely used:

Lichens do not cause any harm to human economic activity.

Summing up all that has been said, we can say that such nondescript and amazing organisms exist next to us. Despite their small size, their benefits are enormous, and for all living organisms, including humans.

After reading this article, you will learn what lichen consists of, what forms of these plants are found, and also about the role they play in nature and in human economic activities. 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, often they are fixed where other living organisms cannot exist. They go north and south farther 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, an arid desert, the back of a beetle, or the bleached bone of a fallen animal. One species (Verrucaria serpuloides) lives by plunging into the icy waters of the Antarctic for a long time, the other (Lecanora esculenta) is carried by the wind. And although in general lichens are very sensitive to any industrial waste, a species such as Lecanora conizaeoides noticeably thrives 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 characterize each of them.

Leafy thrive in areas with abundant rainfall. As you may have guessed, they are named so because they are shaped like leaves. One of their species is shown in the photo below.

The next group is scale (crustal). They are drought tolerant and therefore predominate in deserts. tightly adhere to the substrate on which they grow. Caloplaca heppiana, for example, is often found on walls and gravestones. This and a number of similar species of plants 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 plants are able to take moisture from the air and are found mainly in humid climate zones. The size and appearance of the plants of interest to us are very diverse. Some of them form threads 2.75 m or more long, while others are no more 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 more about what lichen consists of. He is one of the most successful examples of mutualism. This term refers to a mutually beneficial partnership that can be established between two heterogeneous organisms.

The algal component is a necessary element of what the 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 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 take another example. Xanthoria parietina (pictured below) is commonly found on rocks along seashores and on walls and rooftops. Its orange saucer-shaped fruiting bodies (apothecia) are almost indistinguishable in structure from the fruiting body of an isolated fungus.

On a section of a lichen, one can see a thin upper layer of densely intertwined fungal hyphae. 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 top one.

lichen growth

They grow very slowly. Most crustose 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. It follows that the large species of these plants have a very respectable age; it is believed that some representatives of some Arctic species are older than 4000 years.

With the help of so-called lichenometry, that is, measurements of lichens, they even determine the age of the surface of rocks. This method was used to determine 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 algae and fungus is well balanced. But the true nature of these relationships is not yet entirely clear.

Metabolism

The photosynthetic alga, like other green plants, provides food for both partners, since the fungus does not have chlorophyll. The simple carbohydrates synthesized by the algae are secreted by the algae and absorbed by the fungus, where they are converted into other carbohydrates. This exchange of carbohydrates underlies 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 start of photosynthesis.

Moisture absorption

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

Use of lichens

Lichens in nature have 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 nesting material, and serve as a refuge for many species of small invertebrates, such as mites, beetles, butterflies and snails. They also benefit people. Extracts from lichens were once used to dye fabrics from which they sewed. From them they received yellow, brown, red and purple
paints. Intermediate colors were obtained by restaining.

(Cetraria islandica) has been used as a cough suppressant for more than two centuries. 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 used in industry. Thus, from the lichen Roccella sp. a special litmus is mined - a chemical indicator that turns red in an acidic environment and blue in an alkaline environment.