Lichens are a special group of organisms consisting of two completely different species. One part of the lichen is a green algae (classified as plants) or blue-green algae (classified as bacteria). The other part of the lichen is the fungus.
Science studies lichens 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 that live in the tundra spread along the ground in a continuous carpet.
The color of lichens varies: from yellow and gray to brown and black.
Based on the shape of the thallus, three types of lichens are distinguished.
Fruticose lichens connected to the surface on which they grow only by their base. Bearded lichen grows in spruce forests, where it hangs from tree branches. Moss (reindeer moss) grows on the soil. If you step on it in dry weather, you will hear a characteristic cracking sound.
Foliaceous lichens found on tree trunks. They look like plates of different colors and shapes. This is how golden-yellow xanthoria grows on aspen. Foliaceous lichens are connected to the substrate by rhizoid-like projections. They are easily separated from the surface.
Crustose lichens(crust lichens) appear as brownish and grayish crusts on rocks and rocks. They grow tightly to the surface, making them difficult to tear off from it.
Lichens are most often considered an example of symbiosis, in which two different organisms benefit from cohabitation.
The body of a lichen is called thallus. It consists of fungal hyphae, between which there are unicellular green algae or blue-green algae.
Such cohabitation allows lichens to live where neither fungi nor algae can live separately. Fungal hyphae provide water and minerals to the algae. The algae provides the fungus with organic substances, which it synthesizes during 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. Thus, the growth of fruticose lichens can be several millimeters per year, and crustose lichens can generally be a fraction of a millimeter. However, lichens live quite a long time (up to 100 years).
Lichens reproduce asexually. The 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 mother 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, they form humus. Lichens also produce 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.
Reindeer moss serves as food for deer in the tundra. It is also used as pet food.
Icelandic moss is consumed by humans.
Litmus (a chemical indicator) and antibiotics are obtained from a number of lichen species.
Oak moss is used in perfumery. It gives persistence to perfume.
Lichens are environmental indicators. They die in polluted air. Therefore, by the absence or presence of lichens in a certain area, one can judge the ecological situation.
Department of lichens occupy a special place in the plant world. Their structure is very peculiar. The body, called a 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.
- Scale, or cortical, attached to the substrate very tightly, forming a crust. This group makes up about 80% of all lichens.
- Leafy, representing a plate similar to a leaf blade, weakly attached to the substrate.
- 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.
Lichens are a unique group of perennial complex organisms, the body of which consists of a fungus and algae. They live in a variety of types of terrestrial biocenoses: in arctic and mountain tundras, forests, steppes, deserts, etc. The substrate for them is stones (epilithic lichens), the bark of tree trunks and branches (epiphytic), soil (epigean), wood, such as ashlar roofs and fences (epixel).
Lichens have been known for a long time. Even the great Theophrastus, the “father of botany” (IV–III centuries BC), gave a description of two lichens - spey and rochella, which were already used to produce aromatic and coloring substances. True, in those days they were often called either mosses, or algae, or even “the chaos of nature” and “the wretched poverty of vegetation.”
About 20,000 species of lichens are now known. The science of lichens is called lichenology. A specific feature of lichens is the symbiosis of two different organisms: a heterotrophic fungus (mycobiont) and an autotrophic algae (phycobiont). In lichen, both of these components enter into a close relationship: the fungus surrounds the algae and can even penetrate their cells. Lichens form special morphological types - life forms that are not found in the individual organisms that compose them. The metabolism of lichens has a specific character: only they produce lichen acids that are not found in other organisms. The methods of reproduction of lichens as integral organisms are also specific.
The thallus (the so-called body of the lichen) is varied in shape, size, color and structure. The color can be white, gray, yellow, orange, green, black; this is determined by the nature of the pigments contained in the hyphal membrane. Pigmentation helps protect the algal component from excessive light. But sometimes the opposite happens: the lichens of Antarctica are colored black, which absorbs heat rays.
Based on the shape of the thallus, lichens are divided into crustose, foliose and bushy.
The thallus of crustose lichens has the appearance of a crust, tightly fused with the substrate by core hyphae. Sometimes it looks like a powdery coating.
Leafy lichen is a plate located horizontally on the substrate and attached to it by hyphae outgrowths - rhizines. The thallus can be whole or dissected, pressed to the substrate or rising above it.
The thallus of spinous lichens looks like a branched erect or pendulous bush or unbranched erect columns. They are attached to the substrate by a short leg, widened at the end by a heel.
According to the anatomical structure, lichens are homeomeric, when algae are scattered throughout the body of the lichen, or heteromeric, when algae form a separate layer in the thallus. The top of the thallus is covered with a crustal layer, consisting of cells fused with their walls and having the appearance of cellular tissue - plectenchyma. The bark plays a protective function and also strengthens the thallus. The attachment organs of foliose lichens are rhizoids and rhizines; the former consist of one row of cells, and the latter - of rhizoids connected into strands.
Lichens reproduce either by spores produced by the fungus, or by pieces of the thallus, that is, vegetatively.
The spores are spread by the wind and, once in favorable conditions, germinate into the hypha, but a new lichen will only form if the hypha encounters a suitable algae.
Vegetatively, lichens reproduce by isidia and soredia - outgrowths on the thallus containing both components of the lichen.
Lichens are extremely widespread around the globe, but their main diversity is found in mountain tundra and mountain forests.
Their role is especially great in the tundra and forest-tundra, where they form a noticeable part of the vegetation cover and where they provide shelter for invertebrates and small vertebrates, food for them and for large vertebrates, such as reindeer. Icelandic moss lichen is used in northern countries as a supplement to pet food and as an additive in bread baking.
In all biogeocenoses, lichens perform photosynthetic and soil-forming functions. Especially during the initial colonization of freshly exposed substrates, rocky, rocky, and poor in organic matter.
The widespread use of lichens in medicine is based on their tonic and antiseptic properties. The lichen acids they produce have antimicrobial activity against staphylococci, streptococci, tubercle bacilli, and are also successfully used in the treatment of dermatitis.
Lichens are sensitive to the presence of harmful impurities in the air, especially those containing heavy metals. This feature is used to map territories by the level of atmospheric pollution. Zones of complete absence of lichens (“lichen deserts”) are observed, for example, in forests adjacent to oil refineries. The use of lichens as convenient indicators of atmospheric pollution is called lichen indication.
Since ancient times, the use of lichens in perfumery has been known, based on the high content of aromatic substances and essential oils in their thalli. In particular, oak moss is used in the manufacture of perfumes.
This group of plants has also been known as dyes for a very long time, and Scottish tweed is still dyed with lichen extracts. The indicator litmus, widely used in chemistry, is also a derivative of lichens.
LICHENS - CHILDREN OF SPACE?
The results of the experiment, carried out on board the Foton-M2 satellite owned by the European Space Agency, left its organizers in amazement: samples of ordinary lichen, which spent more than two weeks in low-Earth orbit, demonstrated absolute insensitivity to the harsh conditions of outer space.
Lichens are able to survive in extreme conditions where ordinary vegetation cannot survive: deserts, steppes and tundra. In terms of adaptability, only primitive extremophile bacteria can compete with lichens, but lichens are at a much higher stage of evolutionary development and have a much more complex structure. That is why lichens are of interest to exobiologists who are looking for extraterrestrial organisms.
The essence of the experiment carried out during the Foton-M2 program was that a container with samples of lichens of the species Rhizocarpon geographicum and Xanthoria elegans was taken outside the protective casing of the Foton-M2 apparatus, opened and left in this form for two weeks. During this entire period, the samples experienced significant temperature fluctuations and were exposed to the full spectrum of solar radiation, including hard ultraviolet radiation, and cosmic radiation. 14 days after the start of the experiment, the container was closed again, placed inside the descent module, and after returning to Earth, it was sent to the Dutch ESA laboratory.
Opening the container showed that all lichens feel great. Their ability to photosynthesize was also not affected at all.
The results of the experiment provide additional arguments to supporters of the theory of panspermia, confirming the assumption that fragments of lichens thrown into space as a result of the impact of a large meteorite and falling, say, on Earth, could well “infect” a potentially suitable planet with the seeds of life and turn on the mechanism of evolution ( however, this does not solve the mystery of the origin of life as a whole in the Universe).
In addition, such an amazing resilience of lichens also suggests that this type of plant could well survive on the surface of Mars.
Lichens
Lichens are usually considered separately from fungi, although they belong to them, being a specialized group. They are quite diverse in appearance and color and number 26 thousand species, united in more than 400 genera.
Lichens are an example of an obligate symbiosis of fungi and algae. According to the nature of sexual sporulation, lichens are classified into two classes: marsupials (reproduce by spores that ripen in pouches), which includes almost all varieties of lichens, and basidial (spores ripen in basidia), numbering only a few dozen species.
Reproduction of lichens is carried out by sexual and asexual (vegetative) methods. As a result of the sexual process, spores of the lichen fungus are formed, which develop in closed fruiting bodies - perithecia, which have a narrow outlet at the top, or in apothecia, wide open towards the bottom. Germinated spores, having encountered algae corresponding to their species, form a new thallus with it.
Vegetative propagation involves the regeneration of the thallus from its small sections (fragments, twigs). Many lichens have special outgrowths - isidia, which easily break off and give rise to a new thallus. Other lichens produce tiny granules (soredia) in which algae cells are surrounded by a dense cluster of hyphae; these granules are easily dispersed by the wind.
Lichens grow on soil (epigean), stones (epilithic) or tree trunks (epiphytic), receiving the moisture necessary for life from the atmosphere. Some species live in the marine littoral zone. When they first settle in barren places, lichens form humus when they die, on which other plants can then settle. Lichens have even been found in barren Arctic deserts and inside Antarctic rocks. Lichens are distributed throughout the world, but are especially diverse in the tropics, highlands and tundra. But in laboratories, lichens die quite quickly. And only in 1980, American scientists were able to “combine” an algae and a mushroom grown from a spore.
Lichens are perennial organisms; they accumulate polysaccharides and fatty acids. Some substances have an unpleasant taste and smell, others are eaten by animals, and others are used in perfumery or the chemical industry. Some lichens are raw materials for making paint and litmus. Perhaps the famous manna from heaven that fed the people of Moses for forty years during his wanderings in the desert was lichen.
Lichens are bioindicator organisms; they grow only in environmentally friendly places, so you won’t find them in big cities and industrial areas.
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 on their systematic position. Some believe that they should be classified as a plant kingdom, while others believe that they should be classified as fungi. Next, we will consider the types of lichens, the features of their structure, their significance in nature and for humans.
General characteristics of lichens
Lichens are a lower 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. There is mutually beneficial cohabitation between these two representatives of the living world.
Lichens, regardless of the variety, are not green in color; most often they can be gray, brown, yellow, orange or even black. This depends on the pigments, as well as 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 determined by historical development.
- Unlike plants or animals, this organism has a specific external and internal structure.
- The physiological processes occurring in fungi 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.
- A special method of reproduction.
- Attitude to environmental factors.
All these features confuse scientists and do not allow them to determine a permanent systematic position.
Varieties of lichens
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:
- Scale lichens. They got their name from their shape, similar to scale.
- Foliaceous lichens. They look like one large leaf blade, hence the name.
- Fruticose lichens resemble a small bush.
Let's look at the features of each type in more detail.
Description of crustose lichens
Almost 80% of all lichens are crustose. In their shape they look like a crust or a thin film, firmly fused with the substrate. Depending on their habitat, crustose lichens are divided into:
Due to its special appearance, this group of lichens can be completely invisible and blend in with the environment. The structure of crustose lichens is unique, so they are easy to distinguish from other species. But the internal structure of almost all is the same, but more on that later.
Habitats of crustose lichens
We have already looked at how crustose lichens got their name, but the question arises: do the habitats differ? 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.
Crustaceous types of lichens are distributed throughout the planet. Depending on the substrate, one or another species predominates. For example, in the Arctic you cannot find species that are common in the taiga, and vice versa. There is a connection to a certain type of soil: some lichens prefer clay, while others feel comfortable on bare rocks.
But among the great diversity of this group of organisms, you can find species that live almost everywhere.
Features of foliose lichens
The thallus of this species looks like medium-sized scales or plates, attached to the substrate using a bunch of fungal hyphae. The simplest thallus resembles a rounded leaf blade, which can reach 10-20 cm in diameter. With this structure, the thallus is called monophyllous. 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
Bushy lichens received this name 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 dimensions 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 being torn off from the substrate in strong winds.
Internal structure of lichens
Almost all types of lichens have the same internal structure. Anatomically, two types are distinguished:
It should be noted that those lichens that belong to crustaceans do not have a lower layer, and the hyphae of the core directly grow together with the substrate.
Feeding features of lichens
Both organisms living in symbiosis take part in the feeding process. 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 perform the function of leaves. Since for the most part lichens settle on lifeless substrates, they absorb moisture over their entire surface; not only rainwater, but also fog and dew are suitable for these purposes.
For normal growth and functioning, lichens, like plants, require nitrogen. If green algae are present as a phycobiont, then nitrogen compounds are extracted from solutions when the thallus is saturated with moisture. It’s easier for lichens, which have blue-green algae; they are able to extract nitrogen from the air.
Reproduction of lichens
Regardless of the variety, all lichens reproduce in the following ways:
Considering that these organisms grow very slowly, we can conclude that the reproduction process is quite long.
Ecological role of lichens
The importance of this group of organisms on the planet is quite great. They are directly involved in the process of soil formation. They are the first to settle in lifeless places and enrich them for the growth of other species.
Lichens do not require a special substrate to function; they can cover barren territory, preparing it for plant life. This is explained by the fact that in the process of life, lichens secrete special acids that contribute to the weathering of rocks and enrichment with oxygen.
Settling on bare rocks, they feel absolutely comfortable there and gradually create favorable conditions for other species. Some small animals are able to change their color to match the color of lichens, thus camouflaging and using them for protection from predators.
The importance of lichens in the biosphere
Currently, more than 26 thousand species of lichens are known. They are distributed almost everywhere, but surprisingly they can serve as an indicator of air purity.
These organisms are quite sensitive to pollution, so in large cities near roads and factories you will hardly find lichens. They simply do not survive there and die. It should be noted that crustose lichens are the most resistant to poor natural conditions.
Lichens also take a direct part in the cycle 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 in trees, these symbiotic organisms cause virtually no harm, since they do not penetrate deep into living tissues. In a way, they can even be called protectors, because a plant covered with lichens is less susceptible to attacks by pathogenic fungi; lichen acids suppress the growth of wood-destroying fungi.
But there is also a downside: if the lichens grow too much and cover almost the entire tree, they cover the lentils, disrupting gas exchange. And this is an excellent refuge for insect pests. 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
We cannot ignore the question of the role of lichens in human life. There are several areas where they are widely used:
Lichens do not cause any harm to human economic activity.
To summarize all that has been said, we can say that such inconspicuous and amazing organisms exist next to us. Despite their small size, their benefits are enormous, for all living organisms, including humans.
