Photobiont usually represented by green algae (One), or cyanobacteria, and mycobiont – marsupials (Ascomycetes) or much less sponk basidiomycetes (Basidiomycetes) fungi. Despite the composite nature of lichens, they are a separate taxonomic group with their species, generic, etc. names, and the name is assigned on mycobiont. Klassificeret lichens in different ways, but currently they are placed in the same group as related mycobiont fungi that do not form lichens. Photobiont retains its taxonomic independence.
According to the structure of the body (of thallus, or thallus) of the lichen are of scale (cortical), foliose and bushy. They are spread across the globe from the tropics to the polar regions. Well-known lichens such as reindeer lichen or reindeer moss (Cladonia rangiferina), and species of Usnea, hangs from the trees like beards and very similar in appearance to flowering epiphytic plants of the genus Tillandsia.
Structure
Lichens are very different colors. Lichens painted in a wide range of colors from white to bright yellow, brown, purple, orange, pink, green, blue, grey, black.
In appearance to distinguish lichens:
Scale. The scale thallus of lichen is a crust ("scale"), the bottom surface tightly fused with the substrate and can not be separated without significant damage. This allows them to live on steep slopes, trees and even concrete walls. Sometimes nakupny lichen develops inside the substrate and on the outside it is not visible.
Foliose. Foliose lichens have the form of plates of different shapes and sizes. They are more or less tightly attached to substratum with the help of the outgrowths of the lower cortical layer.
Bushy. The most difficult from the point of view of the morphology of bushy lichens the thallus forms a plurality of flat or rounded branches. Grow on the ground or hanging from trees, wood residues and rocks.
Symbiosis, i.e. cohabitation of photobiont and fungus, occurs if they are compatible types meet randomly. The formation of lichens is possible in this way to cause and in the laboratory. It is possible to observe how the growing filaments (hyphae) of the fungus entwine cells photobiont, and their mass (mycelium) isolate the algae cells from the external environment.
After the occurrence of such an Association element within the body, but rather his mycobiont forms the thallus of a specific structure that is not found even among taxonomically close the fungi living separately from photobiont. Appear structures similar to those characteristic of the stems and leaves of flowering plants. Primarily, this bark is an isolated superficial layer of tightly interwoven hyphae, allowing the lichens to quickly absorb the surrounding moisture in wet weather and also dry quickly, which saves the cells from overheating and hypothermia. As completely impermeable sheath would prevent gas exchange in the cortex, there are simple pores and cracks, and areas with loosely arranged cells resembling lenticels in the bark of trees. Some genera of lichens are highly specialized pores called cifelli and pseudocipher, largely similar in structure with the stomata on the leaves of plants. Under the bark is more powerful layer of loosely interwoven hyphae between cells of the algae. This is the core of the lichen. Usually cells photobiont concentrated on its periphery – closer to the light, forming more or less pronounced photosynthetic layer. Many lichens thallus are tightly appressed to the substratum, the crust is formed only on the upper side, and the gas probably goes directly through the core. The more difficult arranged species, in particular lichens bushy, formed a special threadlike outgrowths that attach them to the substrate like plant roots. If these outgrowths are formed by the hyphae of the lower cortex, they are called rhizoids, and if they are thicker and include medullary hyphae – rubbers. However, their absorptivity significant role in the life of lichens is not playing.
Lichens are perennial organisms, they accumulate spare substances in the form of polysaccharides or other compounds related to carbohydrates (e.g. charsperrow). In the crust and the core lichens are formed by a complex of fatty acid and derivatives of such compounds, as orcinol and anthraquinone. Some of these substances, unpleasant taste and do lichens inedible for animals. Others, very pleasant aroma, are used in the perfume industry, and some for the production of dyes. The ability to synthesize certain compounds important systematic characteristic lichens.
A number of lichens food addiction fungus from photobiont may not be complete, and mycobiont receives a portion (at least – most) of the necessary nutrients as a parasite, taking root with its hyphae into living mosses or other lichens. Some lichens containing as photobionts cyanobacteria of the genera Nostoc and Calothrix, capable of "locking" and use atmospheric nitrogen. When lichens of the genus Peltigera, including green algae, cyanobacteria, face, gifs of mycobiont (generally the crust) quickly surround her, forming a special surface vessel, cephalodia from which the body receives additional nitrogen nutrition. A lichen genus Stereocaulon such alien photobiont, although isolated on the surface of the thallus, connects a loose bundle of hyphae from the core, and in some species of the genus Lobaria cephalodia internal.