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 symbiots
They are distributed throughout the earth and can grow equally well both in cold rocky terrain and in hot deserts. Their coloring can be of the most diverse color: red, yellow, white, blue, brown, black. The mechanism of lichen formation is not fully understood. But it can be said with accuracy that sunlight affects their formation. There are scale, bushy and leafy lichens. Thalli of the former are similar to a crust that snugly adheres to 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 that grow vertically and can reach several meters in height. But in this article we will examine in detail the second species of organisms, the appearance and structure of leafy lichens, resembling tree leaves in their form .
What are the structural elements
The thallus or thallus is an integral part of unicellular or multicellular mushrooms, mosses and lichens. Compared to plants, for them it is their young green branches. Tallomas can be leafy or bushy.
Gifa is a filamentous formation resembling a web. It is multicore and multicellular. And it is designed to absorb nutrients, water and, like a web, can serve to catch other organisms (for example, in predator fungi).
Substrate is the surface to which the object is attached. It is also a breeding ground for some plants and lichens.
Appearance of leafy lichens
Their thallus is rounded, leaf-shaped and lamellar, sometimes consisting of one or several parts. And gifs grow along the edges or along the radius of the circle. Leafy lichens have the form of a layered plate located on a substrate in a horizontal manner. The correct shape of the thallus depends on the surface of the substrate. The smoother it is, the more round the lichen will look rounded.
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 leafy lichens are somewhat faster than other varieties. In addition, they are centenarians. Some thalli are over a thousand years old. There is a direct correlation between the immobility of the substrate and the lifespan of the lichen.
Structure
Leafy lichens have a two-level thallus, due to their dorsovertral 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. By 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 distinguishable:
- 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 an air cushion is formed. It supplies oxygen to the constituent parts of the lichen, carrying out gas exchange, and promotes the accumulation and preservation of moisture. Gyph consists of special attaching organelles - a rhizoid.
The thallus is from one plate, then it is monophilic, or from several layers and is called polyphilic. The latter have no legs, their base is firmly attached to the surface, so they hold on to the substrate more firmly. They are not afraid of winds, hurricanes and other bad weather. Tall can be dissected into lobes, cut along the edges, divided into blades. Sometimes the appearance of a lichen resembles a complexly woven lace fabric.
Spread
Leafy lichens grow in areas with high rainfall. They are easy to spot 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 ancient buildings. They grow along roads, in swamps, edges, and dry meadows. Basically, their geographical location is precisely due to the choice of substrate. With environmental degradation, lichens often change color closer to dark and gray. Ground organisms grow especially magnificent, covering vast areas of the earth. These include deer moss (Cladonia forest).
Types of leafy lichens
Across the globe, more than 25 thousand species of lichens are distributed. If organisms are divided according to the substrate to which they prefer to attach, then there are:
- Epigenea - located on the soil or sand (for example, brown Parmelia, Nephrom Hypogymnia, Solorin).
- Epilithic - fastened to stones, rocks (Gyrophora, Collem, Xanthoria, Cetraria).
- Epiphytic - grow on trees and bushes, mainly on leaves and trunks (Parmelia, Fiscia, Cetraria, Lobaria, Candelaria).
- Epixillary - located on dead trees, stumps without bark, walls of old buildings (Hypogymnia, Parmeliopsis, Xanthoria).
It must be remembered that the same genus can include species with leafy thalli, as well as bushy, or their intermediate forms.
Lichen Parmelia
In its internal structure, it is very similar to green algae. Its surface may be yellow, brown in color with the presence of green, black and white blotches. The genus Parmelia is a leafy lichen, which has about 90 species only in Russia, has been cut into large parts by thallus. Its lobes can be either narrow or wider. It grows equally well on tree trunks and on stones, adapts to a polluted urban climate. The shape of this living organism is so diverse that confirms the fact that it is not always advisable to classify lichens only by their appearance. During World War II, parmelia powder was used to stop blood from being injured. It was also added to flour to protect it from pests and increase shelf life.
Leafy lichens, the names of which are determined not only by the structure and form, but also by the aureole, type of substrate, are very diverse. Many of them are used in the food industry. They feed cattle and small cattle. Recently, a powder of them is widely used as food additives that make up pharmaceutical preparations. Cetraria, for example, are used in the manufacture of anti-diarrhea drugs, to stimulate the immune system, normalize the digestive tract, and it is also part of many antiviral drugs.