What are lichens. Scale lichens: description, structure, meaning in nature

Lichens are a special group of organisms consisting of two completely different species. One part of a lichen is green algae (belongs to plants) or blue-green algae (belongs to bacteria). The other part of a lichen is a fungus.

Lichens are studied by science lichenology which is considered a branch of botany.

There are more than 25 thousand species of lichens.

Lichens are unpretentious and therefore widespread. They can be found even in permafrost conditions or on bare rocks. They can grow on tree trunks and the ground. Lichens living in the tundra spread along the ground in a continuous carpet.

The color of lichens varies from yellow and gray to brown and black.

According to the shape of the thallus, three types of lichens are distinguished.

fruticose lichens connected to the surface on which they grow, only at their base. Bearded lichen grows in spruce forests, where it hangs from tree branches. Reindeer moss (reindeer moss) grows on the soil. If you step on it in dry weather, you will hear a characteristic crack.

foliose lichens found on tree trunks. They look like plates of different colors and shapes. So golden-yellow xanthoria grows on aspen. Leafy lichens are connected to the substrate by rhizoid-like outgrowths. They are easily removed from the surface.

scale lichens(crustal lichens) appear as brownish and greyish crusts on stones and rocks. They adhere tightly to the surface, as a result of which it is difficult to tear them off from it.

Lichens are most often considered an example of symbiosis, in which cohabitation is beneficial for two different organisms.

The body of a lichen is called thallus. It consists of fungal hyphae, between which are single-celled green algae or blue-green algae.

Such cohabitation allows lichens to live where neither fungi nor algae can live separately. The hyphae of the fungus provide the algae with water and minerals. Algae provides the fungus with organic substances that it synthesizes in the process of photosynthesis.

Since algae have to feed not only themselves, but also the fungus, lichens grow very slowly. Also, often, growing in places with permafrost, lichens do not receive enough water. So the growth of bushy lichens can be several millimeters per year, and scale - in general, fractions of a millimeter. However, lichens live long enough (up to 100 years).

Lichens reproduce asexually. Algae cells divide into two, and the fungus forms spores. Also, special groups of cells can form in the lichen thallus. These groups leave the parent lichen and give rise to a new organism in a new place.

The meaning of lichens

Lichens are the first to colonize places where there is no soil. Gradually dying off, they form humus. Also, lichens secrete acids, which leads to the destruction of rocks. As a result of mixing destroyed rocks and humus, soil is formed on which plants can grow.

Yagel serves as food for deer in the tundra. It is also used as pet food.

Icelandic moss is eaten by humans.

From a number of lichen species, litmus (a chemical indicator) and antibiotics are obtained.

Oak moss is used in perfumery. It gives strength to spirits.

Lichens are ecological indicators. They die in polluted air. Therefore, by the absence or presence of lichens in a certain area, one can judge the ecological situation.

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.

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Lichens are a symbiosis of a fungus and algae, i.e., 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 hyphae of the fungus form the basis of the thallus, forming the lower crust attached to the substrate, and the surface crustal layer, causing the shape and color of the lichen.

Seaweed occupying cavities between hyphae,form the gonidial layer.

Under a layer of algae, fungal hyphae are located loosely, 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. Bundles of hyphae (rhizoids) pass through the lower cortex from the core, which attach the lichen to the substrate.

Crustose lichens do not have a lower bark, and the fungal hyphae of the core grow together directly with the substrate.

Rice. Lichen structure

Bark functions:

• protective;
• support;
• attaching (nand rhizoids form in the lower crustal layer);
• gas exchange (through perforations (dead areas of the crustal layer), cracks and breaks in the crustal layer).

Algae zone function:

• photosynthesis;
• accumulation of organic matter.

Core function:

• conducting air to algae cells;
• support function (atsome bushy lichens).

Lichens form mainly:

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

The essence of symbiosis:

• Algae gives the fungus organic substances obtained during photosynthesis.
• The fungus, having an extensive mycelium, provides the algae with water and minerals.

Such symbioses of certain types of fungus and algae are so stable that they are perceived as a certain type of organism.

Lichen classification

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

• scale: attached to the substrate with its entire surface (rhizocarpon);
• leafy: attached to the substrate at separate points (parmelia, xanthoria).
  In some leaf lichens, the thallus is attached with a short stalk. (gomfa), located in the central part of the thallus.
• bushy: attached at one point and branching (cladonia, reindeer moss, sleeping).
  Bushy radially built lichens have a bark on the periphery of the transverse section, a gonidial layer under it, and a core inside.
  Crustaceous lichens grow with their periphery, and fruticose ones grow with the ends of "twigs".

Rice. Scale lichen Fig. leafy lichen

Rice. fruticose lichen

Lichen reproduction

Lichens have vegetative, sexual and asexual reproduction.

Asexual reproduction:

• fragmentation;
• soredia- microscopic glomeruli, consisting of one or more algae cells surrounded by fungal hyphae; are formed inside the thallus, and after maturation they come to the surface and burst, scattering diaspores;
• isidia- small, variously shaped outgrowths of the upper surface of the thallus, breaking off when ripe.

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

Sexual reproduction:

• the formation of fruiting 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 for a number of years the fruiting body is able to produce spores. A lot of spores form, but not all of them germinate. For germination, conditions are needed, primarily 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 substances.

The lichens of tropical forests have the highest growth rate, the inhabitants of rocks and tundra have the lowest.

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

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

Interestingly, the age of the thallus is often several hundred and thousands of years.

The meaning of lichens

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

Human use of lichens:

• lichens are food for tundra reindeer herding;
• some types of lichens are eaten;
• are raw materials for the production of dyes (for example, litmus);
• used in folk medicine (for example, sleeping);
• are used in environmental monitoring due to their high sensitivity to chemical pollutants.

And cyanobacteria. The name of the organisms comes from the similarity of their appearance with some skin diseases, and is translated from Latin as "lichen".

Description of symbiotes

They are distributed throughout the earth and can grow equally well both in cold rocky terrain and in hot deserts. Their color can be of the most varied colors: red, yellow, white, blue, brown, black. The mechanism of lichen formation is not fully understood. But with accuracy we can say that their formation is influenced by sunlight. There are also leafy lichens. The thalli of the former are similar to a crust that adheres tightly to the substrate. They are small (up to 2-3 cm), merge with each other, grow on the surface of tree trunks, rocks, forming conglomerates with a diameter of tens of centimeters. Bushy - more developed organisms that grow vertically and can reach several meters in height. But in this article we will take a closer look at the second variety of organisms, the appearance and structure of foliose lichens, reminiscent of their trees.

What are the structural elements

Thallus or thallus is an integral part of unicellular or multicellular fungi, mosses and lichens. If compared with plants, then for them it is their young green branches. The thalli may be leaf-shaped or bushy.

Hypha is a filamentous formation resembling a web. It is multinucleated and multicellular. And it is intended to absorb nutrients, water and, like a web, can serve to catch other organisms (for example, in predatory mushrooms).

The substrate is the surface to which the object is attached. It is also a breeding ground for some plants and lichens.

foliose lichens

Their thallus is rounded, leaf-shaped and lamellar, sometimes consisting of one or more parts. And hyphae grow along the edges or along the radius of the circle. Leafy lichens have the form of a layered plate located on the substrate in a horizontal manner. The correctness of the shape of the thallus depends on the surface of the substrate. The smoother it is, the more rounded the lichen will look.

It is attached to the base with the help of a thick short leg located in the center of the thallus. The plate itself with a diameter of no more than 20-30 cm is quite dense and leathery. Its shade can vary from dark green or gray to brown and black. They grow very slowly, but foliose lichens are somewhat faster than other varieties. In addition, they are long-lived. Some thalli are over a thousand years old. There is a direct relationship between the immobility of the substrate and the life span of the lichen.

Structure

Leafy lichens have a two-level thallus due to their dorso-vertral structure. That is, they have an upper and lower surface. The upper part is rough or even, sometimes covered with outgrowths, tubercles and cilia, warthogs. On the bottom there are organs with which the lichen is attached to the substrate. In structure, it can also be smooth or uneven. Both parts differ not only in shape, but also in color intensity.

Under the microscope, four main anatomical layers are clearly visible:

• upper cow;
• algal;
• core;
• lower cow.

Leafy lichens are loosely attached to the surface of the substrate and are easily separated from it. But between the thallus and the base, it is formed. It nourishes the constituent parts of the lichen with oxygen, carrying out gas exchange, and contributes to the accumulation and preservation of moisture. The hyphae consists of special attachment organelles - rhizoids.

The thallus can be from one plate, then it is monophilic, or from several layers and is called polyphilic. The latter do not have a leg, their base is firmly attached to the surface, so they hold onto the substrate more firmly. They are not afraid of winds, hurricanes and other bad weather. The thallus can be dissected into lobes, cut along the edges, divided into lobes. Sometimes the appearance of a lichen resembles an intricately woven lace fabric.

Spreading

Leafy lichens grow in areas with high rainfall. They are easy to find on all continents, including even cold Antarctica. They can be placed on bare stones and rocks, on the trunks of shrubs and trees, mossy stumps, on old buildings. They grow along roads, in swamps, edges and dry meadows. Basically, their geographical location is precisely due to the choice of substrate. With the deterioration of the environment, lichens often change color closer to dark and gray. Ground organisms grow especially luxuriantly, covering vast areas of the earth. These include (Kladonia forest).

Types of foliose lichens

More than 25 thousand species of lichens are distributed throughout the globe. If you divide organisms according to the substrate to which they prefer to attach, then there are:

• Epigeic - located on soil or sand (for example, Parmelia brown, Hypohymnia Nephrom, Solorina).
• Epilithic - attached to stones, rocks (Gyrofora, Collem, Xanthoria, Cetraria).
• Epiphytic - grow on trees and bushes, mainly on leaves and trunks (Parmelia, Fiscia, Cetraria, Lobaria, Candelaria).
• Epixial - located on dead trees, stumps without bark, walls of old buildings (Hypohymnia, Parmeliopsis, Xanthoria).

It must be remembered that the same genus may include species with both foliose thalli and fruticose, or their intermediate forms.

Lichen Parmelia

In its internal structure, it is very similar to green algae. Its surface can be yellow, brown with green, black and white patches. The genus Parmelia is a leafy lichen, which has about 90 species only in Russia, has a thallus cut into large pieces. Its blades can be both narrow and wider. It grows equally well on tree trunks and on stones, and adapts to the polluted urban climate. The form of this living organism is so diverse that it confirms the fact that it is not always advisable to classify lichens only in appearance. During World War II, parmelia powder was used to stop bleeding from wounds. It was also added to flour to protect it from pests and increase shelf life.

Leafy lichens, whose names are determined not only by the structure and shape, but also by the habitat halo, the type of substrate, are very diverse. Many of them are used in the food industry. They are fed large and. Recently, the powder of them is widely used as food additives that make up pharmaceutical preparations. Cetraria, for example, is used in the manufacture of anti-diarrhea remedies, to stimulate the immune system, to normalize the organs of the digestive tract, and it is also part of many antiviral drugs.

Department of lichens occupy a special place in the plant world. Their structure is very peculiar. The body, called the thallus, consists of two organisms - a fungus and an algae, living as one organism. Bacteria have been found in some types of lichens. Such lichens are a triple symbiosis.

The thallus is formed by the interweaving of fungal hyphae with algae cells (green and blue-green).

Lichens live on rocks, trees, soil, both in the North and in tropical countries. Different types of lichens have different colors - from gray, yellowish, greenish to brown and black. Currently, more than 20,000 species of lichens are known. Lichens are studied by a science called lichenology (from the Greek "leuchen" - lichen and "logos" - science).

According to morphological features (appearance), lichens are divided into three groups.

1. Scale, or crusty, attached to the substrate very tightly, forming a crust. This group makes up about 80% of all lichens.
2. Leafy, which is a plate similar to a leaf blade, loosely attached to the substrate.
3. Bushy, which are free small bushes.

Lichens are very hardy plants. They grow in the most barren places. They can be found on bare rocks, high in the mountains, where other plants do not live. Lichens grow very slowly. For example, "reindeer moss" (moss moss) grows by only 1 - 3 mm per year. Lichens live up to 50 years, and some up to 100 years.

Lichens reproduce vegetatively, by pieces of the thallus, as well as by special groups of cells that appear inside their body. These groups of cells are formed in multitudes. The body of a lichen is torn under the pressure of their overgrown mass, and groups of cells are carried by wind and rain streams.

Lichens play an important role in nature and in economic activity. Lichens are the first plants to settle on rocks and similar barren places where other plants cannot live. Lichens destroy the surface layer of the rock and, dying, form a layer of humus, on which other plants can already settle.

Yagel, or “reindeer moss”, is more nutritional than potatoes and is the main food for reindeer, able to get them out from under the snow cover. Deer give people milk, meat, wool, skin and are used as draft animals.

Some types of lichens are used medicinally: Icelandic lichen, or "Icelandic moss", is rich in vitamin C and serves as a remedy for scurvy (gum disease), parmelia is used to protect wounds from suppuration. An edible lichen grows in the deserts: it looks like lumps that can be rolled by the wind over long distances and be a valuable find for a caravan in the desert. This lichen is called manna. Icelandic lichen is used in Iceland as food for people: bread and porridge are prepared from it. Some types of lichens are used in perfumery to give perfumes longevity. Litmus is made from some types of lichens.

The abundance of lichens testifies to the clean air in the area, since they cannot stand the soot and smoke of urban air, therefore they are practically absent along highways and highways and are rarely found in large cities.