Lichens belong to the symbiotic group of fungi, green algae 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 the cold rocky terrain and in hot deserts. Coloring them can be the most diverse colors: red, yellow, white, blue, brown, black. The mechanism of lichen formation has not been studied to the end. But it can be said with certainty that sunlight influences their formation. There are scale, bushy and leafy lichens. The thallus of the first is similar to a crust that fits snugly against the substrate. They have a small size (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, which grow vertically and can reach several meters in height. But in this article we will consider in detail the second species of organisms, the appearance and structure of leafy lichens, reminiscent of their form of leaves of trees.
What are the structural elements
Thallus or thallus is a constituent part of unicellular or multicellular fungi, mosses and lichens. If to compare with plants, then for them it is their young green branches. Tallomas can be leafy or bushy.
Gifa is a filiform formation resembling a web. It is multi-nuclear and multicellular. And it is designed to absorb nutrients, water and, like a web, can serve for catching other organisms (for example, in predator fungi).
Substrate - the surface to which the object is attached. It is also a nutrient medium for some plants and lichens.
Appearance of leafy lichens
The thallus is round in shape, leaf-shaped and lamellar, sometimes consisting of one or more parts. Hyphae grow along the edges or along the radius of the circumference. Lichen lichens have the appearance of a lamellar plate located horizontally on the substrate. The correctness of the shape of the thallus depends on the surface of the substrate. Than it is more equal, the more rounded will look a lichen.
It is attached to the base with 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 leafy lichens are somewhat faster than other species. In addition, they are long-livers. Some thalli have an age of more than a thousand years. There is a direct relationship between the immobility of the substrate and the life span of the lichen.
Leafy lichens have a two-level thallus, due to their dorsovetral 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 lower 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 major anatomical layers are clearly distinguishable:
- Upper cow;
- Lower cow.
Leafy lichens loosely attached to the surface of the substrate and are easily separated from it. But between the thallus and the base an air cushion is formed. It feeds oxygen constituent parts of the lichen, carrying out gas exchange, and contributes to the accumulation and preservation of moisture. Gyphus consists of special attachment organoids - rhizoid.
Thallus is 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 densely grown to the surface, so they hold tightly on the substrate. They are not afraid of winds, hurricanes and other bad weather. Thallus can be cut into lobes, cut at the edges, divided into lobes. Sometimes the appearance of the lichen resembles a complexly woven lace fabric.
Leafy lichens grow in areas where a large amount of precipitation falls. They are easy to detect on all continents, including even cold Antarctica. They can be placed on bare stones and rocks, on trunks of bushes and trees, moss-covered stumps, on ancient buildings of buildings. They grow along roads, in marshes, fringes and dry meadows. In general, their geographical location is due to the choice of substrate. With the deterioration of the ecology, lichens often change color closer to dark and gray. Soil organisms grow especially richly, covering huge areas of land. These include reindeer moss (Cladonia forest).
Types of leafy lichens
More than 25 thousand species of lichens are distributed around the globe. If you divide organisms along the substrate to which they prefer to attach, then there are:
- Epigene - located on soil or sand (for example, Parmelia Brown, Hypogymnia Nephroma, Solorina).
- Epilithic - are attached to rocks, rocks (Gyrofor, Collem, Xantoria, Cetraria).
- Epiphytic - grow on trees and bushes, mostly on leaves and trunks (Parmelia, Fisia, Cetraria, Lobaria, Candelaria).
- Epixial - located on dead trees, stumps without bark, walls of old buildings (Hypogymnia, Parmeliopsis, Xantoria).
It must be remembered that the same genus can include species with both leafy thalli, and with bushy, or their intermediate forms.
In its internal structure, it is very similar to green algae. Its surface can be yellow, brown with the presence of green, black and white impregnations. The genus Parmelia - lichen lichen, which has about 90 species only in Russia, has a cut thallus. Its blades can be either narrow or wider. It grows equally well on tree trunks and on rocks, adapting to the polluted urban climate. The form of this living organism is so diverse that it is confirmed by the fact that it is not always expedient to classify lichens only in appearance. During World War II, parmelia powder was used to stop blood from being injured. Also, it was added to the flour to protect it from pests and extend the shelf life.
Leafy lichens, whose names are determined not only by structure and form, but also by the halo of habitat, by the type of substrate, are very diverse. Many of them are used in the food industry. They are fed large and small cattle. Recently, the powder from them is widely used as food additives that make up pharmaceutical preparations. Cetrariums, for example, are used in the manufacture of anti-diarrhea drugs, to stimulate the immune system, normalize the digestive tract, and it is part of many antiviral drugs.