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 are found in some types of lichens. Such lichens represent 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. The science that studies lichens is called lichenology (from the Greek “leichen” - lichen and “logos” - science).

Based on morphological characteristics (appearance), lichens are divided into three groups.

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

Lichens are very unpretentious plants. They grow in the most barren places. They can be found on bare rocks, high in the mountains, where no other plants 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 large numbers. The body of the lichen breaks under the pressure of their overgrown mass, and groups of cells are carried away by wind and rain streams.

Lichens play an important role in nature and in economic activities. 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 settle.

Reindeer moss, or “reindeer moss,” is more nutritious than potatoes and is the main food for reindeer, which are able to reach them from under the snow cover. Deer provide humans with milk, meat, wool, leather and are used as draft animals.

Some types of lichens are used in medicine: Icelandic lichen, or “Icelandic moss,” is rich in vitamin C and serves as a cure for scurvy (gum disease), parmelia is used to protect wounds from suppuration. Edible lichen grows in deserts: it looks like lumps that can be blown over long distances by the wind 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 impart longevity to perfumes. Litmus is made from some types of lichens.

The abundance of lichens indicates clean air in a given area, since they do not tolerate soot and smoke from city air, so they are practically absent along highways and highways and are rarely found in large cities.

- (Lichenes), organisms formed by the symbiosis of a fungus (mycobiont) and algae (phycobiont); traditionally belong to lower plants. Early fossils of L. are presumably attributed to the top. chalk. Occurred as a result of the transfer of certain representatives... ... Biological encyclopedic dictionary

Organisms that are a symbiosis of a fungus (mycobiont) and algae (phycobiont). In L., apparently, there is no strict selectivity between partners; a fungus can exist with different types of algae, and algae can exist with different fungi.... ... Dictionary of microbiology

LICHENS- LICHENS, lichens, Lichenes, a peculiar class of lower plants, consisting of a fungus and algae, together forming one organism. Lichen fungi, with minor exceptions, are marsupials. Algae of L. have the common old name of gonidia. Not… … Great Medical Encyclopedia

Polyphyletic group of fungi Ernst Heinrich Haeckel ... Wikipedia

- (Lichenes) a specialized group of fungi that are in constant cohabitation with algae; Some botanists consider L. as an independent group of lower plants. The science of L. is called lichenology (See Lichenology).... ... Great Soviet Encyclopedia

lichens- ▲ lower plants lichens are symbiotic organisms formed by a fungus and an algae. moss, reindeer moss. Cladonia. cetraria. | manna. soredia. | lichenology. cover up. mossy. moss. mossy (# stump) ... Ideographic Dictionary of the Russian Language

lichens- kerpės statusas T sritis ekologija ir aplinkotyra apibrėžtis Organizmų grupė, kurių kūnas sudarytas iš grybo ir dumblio simbiozės. atitikmenys: engl. lichens vok. Flechten, f; Lichenen rus. lichens, m... Ekologijos terminų aiškinamasis žodynas

Resin moss, spore plants, in which fungi and algae coexist in the body. Fungal cells and algae cells exchange nutrients through assimilation: the former provide water and minerals and receive organic substances from the latter... ... Agricultural dictionary-reference book

Lichens are unique complex organisms, the thallus of which is a combination of a fungus and an algae that are in a complex relationship with each other, more often in symbiosis. Over 20 thousand species of lichens are known.

They differ from other organisms, including free-living fungi and algae, in shape, structure, nature of metabolism, special lichen substances, methods of reproduction, and slow growth (from 1 to 8 mm per year).

Structural features

Thallus lichens consists of intertwined fungal threads - hyphae, and algae cells (or threads) located between them.

There are two main types of microscopic structure of the thallus:

• Homeomeric;
• heteromeric.

On a cross section of a lichen homeomeric type there is an upper and lower cortex, which consists of a single layer of fungal cells. The entire internal part is filled with loosely arranged fungal threads, between which are located algae cells without any order.

In lichen heteromeric type of algae cells are concentrated in one layer, which is called gonidial layer. Below it is the core, consisting of loosely arranged threads of the fungus.

The outer layers of the lichen are dense layers of fungal filaments called cortical layers. With the help of fungal threads extending from the lower cortical layer, the lichen is attached to the substrate on which it grows. In some species, the lower bark is absent and it is attached to the substrate by pith threads.

The algal component of lichen consists of species belonging to the blue-green, green, yellow-green and brown divisions. Representatives of 28 genera of them enter into symbiosis with fungi.

Most of these algae may be free-living, but some are found only in lichens and have not yet been found in a free state in nature. While in the thallus, the algae change greatly in appearance, and also become more resistant to high temperatures and can withstand prolonged drying. When cultivated on artificial media (separately from fungi), they acquire the appearance characteristic of free-living forms.

The thallus of lichens is varied in shape, size, structure, and colored in different colors. The color of the thallus is due to the presence of pigments in the hyphal membranes and fruiting bodies of lichens. There are five groups of pigments: green, blue, violet, red and brown. A prerequisite for the formation of pigments is light. The brighter the lighting in places where lichens grow, the brighter they are colored.

The shape of the thallus can also be varied. According to the external structure of the thallus, lichens are divided into:

• Scale;
• leafy;
• bushy.

U crustose lichens the thallus has the appearance of a crust, tightly fused with the substrate. The thickness of the crusts varies - from barely noticeable scale or powdery deposits to 0.5 cm, diameter - from a few millimeters to 20-30 cm. Scale species grow on the surface of soils, rocks, the bark of trees and shrubs, and exposed rotting wood.

Foliose lichens have the shape of a leaf-shaped plate located horizontally on the substrate (parmelia, wall goldenrod). Usually the plates are round, 10-20 cm in diameter. A characteristic feature of leafy species is the unequal color and structure of the upper and lower surfaces of the thallus. In most of them, on the lower side of the thallus, organs of attachment to the substrate are formed - rhizoids, consisting of hyphae collected in cords. They grow on the surface of the soil, among mosses. Foliage lichens are more highly organized forms compared to crustose lichens.

Fruticose lichens have the form of an erect or hanging bush and are attached to the substrate by small sections of the lower part of the thallus (cladonia, Icelandic lichen). In terms of level of organization, bushy species are the highest stage of thallus development. Their thalli come in different sizes: from a few millimeters to 30-50cm. Hanging thalli of fruticose lichens can reach 7-8 m. An example is the lichen that hangs in the form of a beard from the branches of larches and cedars in taiga forests (bearded lichen).

Reproduction

Lichens reproduce mainly by vegetative means. In this case, pieces are separated from the thallus, carried by wind, water or animals and, under favorable conditions, give rise to new thalli.

In leafy and fruticose lichens, for vegetative propagation, special vegetative formations are formed in the surface or deeper layers: soredia and isidia.

Soredia look like microscopic glomeruli, each of which contains one or more algae cells surrounded by fungal hyphae. Soredia are formed inside the thallus in the gonidial layer of foliose and fruticose lichens. The formed soredia are pushed out of the thallus, picked up and carried by the wind. Under favorable conditions, they germinate in new places and form thalli. About 30% of lichens reproduce by soredia.

Nutrition

The nutritional characteristics of lichens are associated with the complex structure of these organisms, consisting of two components that receive nutrients in different ways. The fungus is a heterotroph, and the algae is an autotroph.

The algae in the lichen provides it organic substances produced by photosynthesis. The lichen fungus receives high-energy products from the algae: ATP and NADP. The fungus, in turn, with the help of filamentous processes (hyphae) acts as a root system. This is how the lichen gets water and mineral compounds, which are adsorbed from the soil.

Lichens are also capable of absorbing water from the environment with their whole body, during fogs and rains. To survive they need nitrogen compounds. If the algal component of the thallus is represented by green algae, then nitrogen comes from aqueous solutions. When blue-green algae act as phycobionts, nitrogen fixation from atmospheric air is possible.

For the normal existence of lichens they are needed in sufficient quantities light and moisture. Insufficient lighting interferes with their development, as photosynthetic processes slow down and the lichens do not receive enough nutrients.

Light pine forests have become the optimal place for their life. Although lichens are among the most drought-resistant species, they still need water. Only in a humid environment do respiratory and metabolic processes take place.

The importance of lichens in nature and human life

Lichens are very sensitive to harmful substances, so they do not grow in places with high dust and air pollution. So, they are used as indicators of pollution.

They take part in the cycle of substances in nature. Their photosynthetic part is capable of producing organic matter in places where other plants cannot survive. Lichens play an important role in soil formation; they settle on lifeless rocky surfaces and, after dying, form humus. This creates favorable conditions for plant growth.

Feeding lichens are an important link in the food chain. For example, deer, roe deer, and moose feed on reindeer moss or moss. Serve as material for bird nests. Lichen manna or Aspicilia edible is used in cooking.

The perfume industry uses them to make perfumes last longer, and the textile industry uses them to dye fabrics. There are also known species with antibacterial properties, which are used in the manufacture of medicines to combat tuberculosis and furunculosis.

Lichens are a very interesting and unique group of lower plants. Lichens (lat. Lichenes) are symbiotic associations of fungi (mycobiont) and microscopic green algae and/or cyanobacteria (photobiont, or phycobiont); the mycobiont forms a thallus (thallus), inside which the photobiont cells are located. The group contains from 17,000 to 26,000 species in about 400 genera. And every year scientists discover and describe tens and hundreds of new unknown species.

Fig.1. Lichen Cladonia stellaris Cladonia stellaris

Lichen combines two organisms with opposite properties: an algae (usually green), which creates organic matter through the process of photosynthesis, and a fungus that consumes this substance.

As organisms, lichens were known to scientists and people long before their essence was discovered. Even the great Theophrastus (371 - 286 BC), “the father of botany,” gave a description of two lichens - Usnea and Rocella. The latter was already used to produce dyes. The beginning of lichenology (the science of lichens) is considered to be 1803, when Carl Linnaeus’ student Eric Acharius published his work “Methodus, qua omnes detectos lichenes ad genera redigere tentavit” (“Methods by which everyone can identify lichens”). He separated them into an independent group and created a system based on the structure of fruiting bodies, which included 906 species described at that time. The first to point out the symbiotic nature in 1866, using the example of one of the species, was the doctor and mycologist Anton de Bary. In 1869, botanist Simon Schwendener extended these ideas to all species. In the same year, Russian botanists Andrei Sergeevich Famintsyn and Osip Vasilyevich Baranetsky discovered that the green cells in lichen are single-celled algae. These discoveries were perceived by contemporaries as “most amazing.”

Lichens are divided into three unequal groups:

1. It includes a larger number of lichens, the class of marsupial lichens, since they are formed by marsupial fungi

2. A small group, class of basidiomycetes, because they are formed by basidiomycetes (less resistant fungi)

3. “Imperfect lichens” got their name due to the fact that fruiting bodies with spores were not found in them

External and internal structure of lichens

The vegetative body of the lichen - the thallus, or thallus - is very diverse in shape and color. Lichens come in a variety of colors: white, pink, bright yellow, orange, orange-red, gray, bluish-gray, grayish-green, yellowish-green, olive-brown, brown, black and some others. The color of the lichen thallus depends on the presence of pigments that are deposited in the membranes of the hyphae, less often in the protoplasm. The richest pigments are the hyphae of the crustal layer of lichens and various parts of their fruiting bodies. Lichens have five groups of pigments: green, blue, purple, red, brown. The mechanism of their formation has not yet been clarified, but it is quite obvious that the most important factor influencing this process is light.

Sometimes the color of the thallus depends on the color of lichen acids, which are deposited in the form of crystals or grains on the surface of the hyphae. Most lichen acids are colorless, but some are colored, and sometimes very brightly - yellow, orange, red and other colors. The color of the crystals of these substances determines the color of the entire thallus. And here the most important factor promoting the formation of lichen substances is light. The brighter the lighting in the place where the lichen grows, the brighter it is colored. As a rule, the lichens of the highlands and polar regions of the Arctic and Antarctic are very brightly colored. This is also due to lighting conditions. The high-mountain and polar regions of the globe are characterized by greater transparency of the atmosphere and high intensity of direct solar radiation, providing significant brightness of illumination here. Under such conditions, a large amount of pigments and lichen acids are concentrated in the outer layers of the thallus, causing the bright color of the lichens. It is believed that the colored outer layers protect the underlying algae cells from excessive light intensity.

Due to low temperatures, precipitation falls in Antarctica only in the form of snow. In this form they cannot be used by plants. This is where the dark color of lichens comes to their aid.

Due to high solar radiation, the dark-colored thalli of Antarctic lichens quickly heat up to a positive temperature even at negative air temperatures. Snow falling on these heated thalli melts, turning into water, which the lichen immediately absorbs. Thus, it provides itself with the water necessary for the processes of respiration and photosynthesis.

As diverse as the thalli of lichens are in color, they are just as diverse in shape. The thallus may have the appearance of a crust, a leaf-shaped blade or a bush. Depending on the appearance, three main morphological types are distinguished:

Scale. The thallus of crustose lichens is a crust (“scale”), the lower surface grows tightly with the substrate and does not separate without significant damage. This allows them to live on steep mountain slopes, trees, and even concrete walls. Sometimes crustose lichen develops inside the substrate and is completely invisible from the outside. As a rule, scale thalli are small in size, their diameter is only a few millimeters or centimeters, but sometimes they can reach 20–30 cm. In nature, one can often observe how small scale scale thalli of lichens, merging with each other, form on a rocky surface large spots on rocks or tree trunks, reaching a diameter of several tens of centimeters.

Leafy. Foliaceous lichens look like plates of different shapes and sizes. They are more or less tightly attached to the substrate with the help of outgrowths of the lower cortical layer. The simplest thallus of foliose lichens has the appearance of one large rounded leaf-shaped blade, reaching a diameter of 10–20 cm. Such a blade is often dense, leathery, colored dark gray, dark brown or black.

Bushy. At the organizational level, fruticose lichens represent the highest stage of development of the thallus. In fruticose lichens, the thallus forms many round or flat branches. They grow on the ground or hang from trees, woody debris, and rocks. The thallus of fruticose lichens has the appearance of an erect or hanging bush, less often of unbranched erect outgrowths. This allows the bushy lichens, by bending the branches in different directions, to occupy the best position in which the algae can make maximum use of light for photosynthesis. The thallus of fruticose lichens can be of different sizes. The height of the smallest ones is only a few millimeters, and the largest ones are 30–50 cm. Hanging thalli of fruticose lichens can sometimes reach colossal sizes.

Internal structure of lichen: crustal layer, gonidial layer, pith, lower cortex, rhizoids. The body of lichens (thallus) is an interweaving of fungal hyphae, between which there is a photobiont population.

Rice. 2. Anatomical structure of the lichen thallus

1 - heteromeric thallus (a - upper crustal layer, b - algae layer, c - core, d - lower crustal layer); 2 - homeomeric thallus of the mucous lichen Collema flaccidum; 3 - homeomeric thallus of the mucous lichen leptogium (Leptogium saturninum) (a - crustal layer on the upper and lower sides of the thallus, b - rhizoids)

Each of the listed anatomical layers of the thallus performs a specific function in the life of the lichen and, depending on this, has a completely specific structure.

The crustal layer plays a very important role in the life of a lichen. It performs two functions at once: protective and strengthening. It protects the inner layers of the thallus from the effects of the external environment, especially algae from excessive lighting. Therefore, the crustal layer of lichens usually has a dense structure and is colored grayish, brown, olive, yellow, orange or reddish. The bark layer also serves to strengthen the thallus. The higher the thallus rises above the substrate, the more it needs strengthening. In such cases, strengthening mechanical functions are often performed by a thick crustal layer. Attachment organs are usually formed on the lower crustal layer of lichens. Sometimes they look like very thin threads, consisting of one row of cells. These threads are called rhizoids. Each such thread originates from one cell of the lower crustal layer. Often several rhizoids are united into thick rhizoidal cords.

In the algae zone, processes of carbon dioxide assimilation and accumulation of organic substances take place. As you know, algae need sunlight to carry out photosynthesis processes. Therefore, the layer of algae is usually located near the upper surface of the thallus, directly under the upper crustal layer, and in vertically standing fruticose lichens also above the lower crustal layer. The algae layer is most often of small thickness, and the algae are placed in it so that they are in almost the same lighting conditions. Algae in the lichen thallus can form a continuous layer, but sometimes the hyphae of the mycobiont divide it into separate sections. To carry out the processes of carbon dioxide assimilation and respiration, algae also require normal gas exchange. Therefore, fungal hyphae in the algae zone do not form dense plexuses, but are located loosely at some distance from each other.

Below the algae layer is the core layer. Typically, the core is significantly thicker than the crustal layer and the algae zone. The thickness of the thallus itself depends on the degree of development of the core. The main function of the core layer is to conduct air to the algae cells containing chlorophyll. Therefore, most lichens are characterized by a loose arrangement of hyphae in the core. Air entering the thallus easily penetrates the algae through the spaces between the hyphae. The core hyphae are weakly branched, with sparse transverse partitions, with smooth, slightly gelatinous thick walls and a rather narrow lumen filled with protoplasm. Most lichens have a white pith, since the hyphae of the pith layer are colorless.

According to their internal structure, lichens are divided into:

Homeomeric (Collema), photobiont cells are distributed chaotically among the fungal hyphae throughout the entire thickness of the thallus;

Heteromeric (Peltigera canina), the thallus in cross section can be clearly divided into layers.

The majority of lichens have a heteromeric thallus. In a heteromeric thallus, the upper layer is cortical, composed of fungal hyphae. It protects the thallus from drying out and mechanical stress. The next layer from the surface is the gonidial, or algal, layer, in which the photobiont is located. In the center is the core, consisting of randomly intertwined fungal hyphae. The core mainly stores moisture and also plays the role of a skeleton. At the lower surface of the thallus there is often a lower bark, with the help of outgrowths (rhizin) the lichen is attached to the substrate. A complete set of layers is not found in all lichens.

As in the case of two-component lichens, the algal component - the phycobiont - of three-component lichens is evenly distributed throughout the thallus, or forms a layer under the upper bark. Some three-component cyanolichens form specialized surface or internal compact structures (cephalodia), in which the cyanobacterial component is concentrated.

Methods of feeding lichens

Lichens represent a complex object for physiological research, since they consist of two physiologically opposite components - a heterotrophic fungus and an autotrophic algae. Therefore, we first have to separately study the life activity of myco- and phycobiont, which is done with the help of cultures, and then the life of the lichen as an integral organism. It is clear that such “triple physiology” is a difficult path of research, and it is not surprising that there is still a lot of mystery hidden in the life activity of lichens. However, the general patterns of their metabolism have still been clarified.

Quite a lot of research is devoted to the process of photosynthesis in lichens. Since only a small part of their thallus (5–10% of the volume) is formed by algae, which nevertheless is the only source of supply of organic substances, a significant question arises about the intensity of photosynthesis in lichens.

As measurements have shown, the intensity of photosynthesis in lichens is much lower than in higher autotrophic plants.

For normal photosynthetic activity, the thallus must contain a certain amount of water, depending on the anatomical and morphological type of lichen. In general, in thick thalli the optimal water content for active photosynthesis is lower than in thin and loose thalli. In this case, it is very significant that many species of lichens, especially in dry habitats, are rarely or at least very irregularly supplied with the optimal amount of intrathallal water. After all, the regulation of the water regime in lichens occurs in a completely different way than in higher plants, which have a special apparatus capable of controlling the receipt and consumption of water. Lichens absorb water (in the form of rain, snow, fog, dew, etc.) very quickly, but passively through the entire surface of their body and partly through the rhizoids of the underside. This absorption of water by the thallus is a simple physical process, such as the absorption of water by filter paper. Lichens are capable of absorbing water in very large quantities, usually up to 100 - 300% of the dry mass of the thallus, and some mucous lichens (collemas, leptogiums, etc.) even up to 800 - 3900%.

The minimum water content in lichens under natural conditions is approximately 2–15% of the dry mass of the thallus.

The release of water by the thallus also occurs quite quickly. Lichens saturated with water in the sun lose all their water after 30–60 minutes and become fragile, i.e., the water content in the thallus becomes below the minimum required for active photosynthesis. This results in a peculiar “arrhythmia” of photosynthesis in lichens - its productivity varies throughout the day, season, and a number of years, depending on general environmental conditions, especially hydrological and temperature.

There are observations that many lichens photosynthesize more actively in the morning and evening hours and that photosynthesis continues in them in winter, and in ground forms even under thin snow cover.

An important component in the nutrition of lichens is nitrogen. Those lichens that have green algae as a phycobiont (and they are the majority) accept nitrogen compounds from aqueous solutions when their thalli are saturated with water. It is possible that lichens take part of the nitrogenous compounds directly from the substrate - soil, tree bark, etc. An ecologically interesting group consists of the so-called nitrophilic lichens, growing in habitats rich in nitrogenous compounds - on “bird stones”, where there is a lot of bird excrement , on tree trunks, etc. (species of xanthoria, physcia, kaloplaka, etc.). Lichens that have blue-green algae (especially nostocs) as a phycobiont are capable of fixing atmospheric nitrogen, since the algae they contain have this ability. In experiments with such species (from the genera Collema, Leptogium, Peltigera, Lobaria, Stykta, etc.), it was found that their thalli quickly and actively absorb atmospheric nitrogen. These lichens often settle on substrates that are very poor in nitrogen compounds. Most of the nitrogen fixed by the algae is sent to the mycobiont and only a small part is used by the phycobiont itself. There is evidence that the mycobiont in the lichen thallus actively controls the absorption and distribution of nitrogen compounds fixed from the atmosphere by the phycobiont.

The rhythm of life described above is one of the reasons for the very slow growth of most lichens. Sometimes lichens grow only a few tenths of a millimeter per year, mostly less than one centimeter. Another reason for the slow growth is that the photobiont, often accounting for less than 10% of the lichen volume, takes upon itself to provide the mycobiont with nutrients. In good conditions with optimal humidity and temperature, such as in foggy or rainy tropical forests, lichens grow several centimeters per year.

The growth zone of lichens in crustacean forms is located along the edge of the lichen, in leafy and bushy ones at each tip.

Lichens are among the longest-lived organisms and can reach ages of several hundred years, and in some cases more than 4,500 years, such as Rhizocacron geographicum, living in Greenland.

Reproduction of lichens

Lichens reproduce either by spores, which are formed by the mycobiont sexually or asexually, or vegetatively - by fragments of the thallus, soredia and isidia.

During sexual reproduction on the thalli of lichens, as a result of the sexual process, sexual sporulations are formed in the form of fruiting bodies. Among the fruiting bodies of lichens, apothecia, perithecia and gasterothecium are distinguished. Most lichens form open fruiting bodies in the form of apothecia - disc-shaped formations. Some have fruiting bodies in the form of a perithecia - a closed fruiting body that looks like a small jug with a hole at the top. A small number of lichens form narrow, elongated fruiting bodies called gasterothecium.

In apothecia, perithecia and gasterothecium, spores develop inside the bags - special sac-like formations. Lichens that form spores in pouches are grouped into the large group of marsupial lichens. They originated from fungi of the ascomycete class and represent the main evolutionary line of development of lichens.

In a small group of lichens, spores are formed not inside the bags, but exogenously, at the top of elongated club-shaped hyphae - basidia, at the ends of which four spores develop. Lichens with such spore formation are united in the group of basidiomycetes.

The female genital organ of lichens, the archicarp, consists of two parts. The lower part is called ascogon and is a spirally twisted hypha, thicker than other hyphae and consisting of 10 - 12 single or multinuclear cells. The trichogyne extends upward from the askogon - a thin elongated hypha that passes through the algae zone and the crustal layer and emerges on the surface of the thallus, rising above it with its sticky tip.

The development and maturation of the fruiting body in lichens is a very slow process that lasts 4–10 years. The formed fruiting body is also perennial, capable of producing spores for a number of years. How many spores can lichen fruiting bodies produce? It is estimated, for example, that in the lichen solorina, 31 thousand bursae are formed in an apothecia with a diameter of 5 mm, and 4 spores usually develop in each bursa. Therefore, the total number of spores produced by one apothecia is 124,000. During one day, from 1200 to 1700 spores are released from such an apothecia. Of course, not all spores ejected from the fruiting body germinate. Many of them, finding themselves in unfavorable conditions, die. For spores to germinate, they first need sufficient humidity and a certain temperature.

Asexual sporulation is also known in lichens - conidia, pycnoconidia and stylospores, which arise exogenously on the surface of conidiophores. In this case, conidia are formed on conidiophores developing directly on the surface of the thallus, and pycnoconidia and stylospores in special containers - pycnidia.

Of the asexual sporulations, lichens most often form pycnidia with pycnoconidia. Pycnidia are often found on the thalli of many fruticose and foliose lichens; less often they can be observed in crustose forms.

In each of the pycnidia, small single-celled spores - pycnoconidia - are formed in large quantities. The role of these widespread sporulations in the life of the lichen has not yet been clarified. Some scientists, calling these spores spermatia and pycnidia spermagonia, consider them male reproductive cells, although there is still no experimental or cytological data proving that pycnoconidia actually participate in the sexual process of lichens.

Vegetative propagation. If crustose lichens, as a rule, form fruiting bodies, then among the more highly organized foliose and bushy lichens there are many representatives that reproduce exclusively by vegetative means. In this case, formations that simultaneously contain fungal hyphae and algal cells are more important for the reproduction of lichens. These are soredia and isidia. They serve to reproduce the lichen as a whole organism. Once in favorable conditions, they directly give rise to a new thallus. Soredia and isidia are more common in foliose and fruticose lichens.

Soredia are tiny formations in the form of dust particles, consisting of one or more algae cells surrounded by fungal hyphae. Their formation usually begins in the gonidial layer. Due to the massive formation of soredia, their number increases, they put pressure on the upper bark, tear it and end up on the surface of the thallus, from where they are easily blown away by any movement of air or washed off with water. Clusters of soredia are called sorals. The presence and absence of soredia and sorals, their location, shape and color are constant for certain lichens and serve as a defining feature.

Sometimes, when lichens die, their thallus turns into a powdery mass consisting of soredia. These are the so-called leprosy forms of lichens (from the Greek word “lepros” - “rough”, “uneven”). In this case, it is almost impossible to identify the lichen.

Soredia, carried by wind and rainwater, once in favorable conditions, gradually form a new thallus. The regeneration of a new thallus from the soredia occurs very slowly. Thus, in species from the genus Cladonia, normal scales of the primary thallus develop from the soredia only after a period of 9 to 24 months. And for the development of a secondary thallus with apothecia it takes from one to eight years, depending on the type of lichen and external conditions.

Isidia are found in fewer lichen species than Soredia and Soralia. They are simple or coral-like branched outgrowths, usually densely covering the upper side of the thallus (see figure). Unlike sorals, isidia are covered on the outside with bark, often darker than thallus. Inside, under the bark, they contain algae and fungal hyphae. Isidia easily break off from the surface of the thallus. Breaking off and spreading with the help of rain and wind, they, like soredia, can, under favorable conditions, form new lichen thalli.

Many lichens do not form apothecia, soredia and isidia and reproduce by sections of the thallus, which are easily broken off from the fragile lichens in dry weather by the wind or animals and are carried by them. The reproduction of lichens by sections of the thallus in the Arctic regions is especially widespread, representatives of the genera Cetraria and Cladonia, many of which almost never form fruiting bodies.



Lichens message 5th grade biology will briefly help you deepen your knowledge in the field of biology. Also, a message on the topic of lichens will tell you a lot of useful information about these unpretentious organisms.

Report on lichens

Lichens is a single organism that contains fungi and unicellular algae. This symbiosis is beneficial for the whole organism: while the fungus absorbs water with dissolved mineral salts, the algae simultaneously produces organic substances from water and carbon dioxide through the process of photosynthesis. Lichen is an unpretentious organism, so it can be found in places where there is no other vegetation. After their vital activity, humus appears, which is important for other plants.

In nature, lichens vary in color and appearance. Often on old spruce trees there are tousled beards of such a lichen as lichen. On the bark of trees, often aspen, rounded orange plates are attached. This is the wall goldenrod lichen. In dry pine forests, deer lichen grows, which is whitish grayish small bushes. In dry weather, this plant makes a crunching noise when you walk on it.

Where do lichens grow?

They are common almost everywhere. Since the plants are not whimsical, they can be found on stones, bare rocks, on fences, on the bark of trees, on the soil. In the tundra and northern regions, lichens occupy large areas. They also grow even high in the mountains.

Types of lichens

Based on their appearance, the following groups of plants are distinguished:

• Bushy. These are the most difficult types. They are formed by many round or flat branches. They grow on the ground or hang from rocks, trees and woody debris.
• Scale. Their thallus (thallus) of mushrooms is called crust. Its lower layer grows very tightly with stone, earth or wood. Therefore, if you try to separate a lichen from the organism on which it has settled, then, most likely, you will not be able to do without damaging the entire plant. Crustose lichens grow on mountain slopes, on trees, and on concrete walls.
• Leafy. Lichens look like plates of different shapes and sizes. They are formed by outgrowths of the cortex and are tightly attached to the organism on which they grow.

The structure of lichens

Lichens have some features due to which they are combined into a separate group. The structural elements are represented by transparent threads with green rounded cells between them. Scientists have discovered that the colorless threads are the mycelium of the fungus, and the green cells are unicellular algae. These two different organisms form a single organism. This symbiosis helps the plant adapt favorably to any environmental conditions. Lichen absorbs and absorbs nutrients and water from everywhere - from the soil, air and even dust. When there is a period of drought, the plant can become so dry that it breaks at the slightest touch. And when the rains come, it comes to life again.