Bryophytes are also called true mosses or bryophytes. All species are united in about 700 genera, which, in turn, make up about 120 families.
Bryophyte department: general characteristics
Representatives of the department are mainly small plants no more than 50 mm long. The only exceptions are aquatic mosses, which can be up to 50 cm long, and epiphytes, which are even longer.
Department belongs to the taxon higher plants. The bryophyte department has about 25 thousand species.
Earlier, in addition to leafy mosses, liver mosses and anthocerot mosses were also included in this department. However, at the moment these taxa are independent divisions. Often, speaking of the combined characteristics of these three departments, they resort to the use of the informal collective term bryophytes (Bryophytes).
Plants of the department, like other representatives of bryophytes, have a certain feature associated with the course of the life cycle: the predominance of the haploid gametophyte over the diploid sporophyte.
History
The characteristic of the mossy department proves that mosses, like other spores, evolved from psilophytes (rhinophytes), which are ancient extinct land plants. The moss sporophyte is thought to be the end result of the reduction process of ancestral branched sporophytes.
However, there is another hypothesis, according to which it is assumed that mosses, together with lycopods and rhinophytes, originated from an even more ancient group of plants. The earliest paleontological finds date back to the end of the Devonian - the beginning of the Carboniferous.
Biological Description
The mossy department is different in that its representatives do not have flowers, roots, or a conducting system. They are characterized by reproduction by spores that ripen in sporophyte sporangia.
The dominant haploid gametophyte in the life cycle is a perennial green plant, often with leaf-like lateral outgrowths and root-like outgrowths (rhizoids). Compared with other groups of higher plants, representatives of the mossy department have a simpler structure. Among the majority of species that have a stem and leaves, there is a minority that has thalli and thalli.
But the leaves and stems of mosses are not real, in scientific language they are called caulidia and phyllidia. Phyllidia are petiolate, arranged in a spiral on the stem. They have a solid plate. The vein is not in all cases
The sporophyte does not have the ability to take root and sits directly on the gametophyte. The sporophyte is represented by three components: a box (sporangium), with spores developing in it;leg (sporophore) on which the box is located; foot providing physiological interaction with the gametophyte.
Mosses have a number of characteristics that distinguish them from all higher plants. This is the absence of roots, which is compensated by the presence of a large number of rhizoids. With their help, the plant is attached to the substrate, and also carries out partial absorption of moisture. Basically, the process of water absorption is carried out in the lower part of the plant.
There are assimilation, conductive, storage and integumentary tissues. But bryophytes do not have true vessels and mechanical tissue, while all higher plants do.
Distribution area
Because of their unpretentiousness, mosses are common on all continents, even in Antarctica, and often grow in extreme habitat conditions.
As a rule, mosses grow in dense clusters. Shaded areas, often in the immediate vicinity of a body of water, are ideal conditions for mosses. But they can also grow in open, dry areas.
The mossy division also includes species that live in freshwater reservoirs. But there are no marine inhabitants among them, although there are several species that settle on the rocks in the coastal strip.
Department of bryophytes: value
In nature:
- are participants in the creation of special biocenoses, especially where they almost completely cover the ground (tundra);
- moss cover accumulates and retains radioactive substances;
- abilityabsorption and retention of a large amount of moisture causes participation in the process of regulating the water balance of landscapes.
In the activities of people:
- contribute to waterlogging of soils, therefore, reduce the efficiency of agricultural land;
- carry out the process of uniform transfer of surface water runoff to underground, which protects the soil from corrosion;
- some species of sphagnum moss are used in medicine as a dressing;
- sphagnum mosses are a source of peat formation.
Classification
Signs of the mossy department, despite their commonality, still allow classifying representatives of the department into several separate groups.
The most numerous group of plants included in the department is the real class (leafy mosses). It includes the subclasses green, sphagnum and andrew mosses.
Green mosses
Green moss habitats are soil, tree trunks, rocks and rooftops, but grow best in damp forests that form a solid carpet.
These plants, included in the mossy department, are quite numerous. The most typical representative can be called Kukushkin flax. Its stems are erect, unbranched, densely covered with narrow linear-lanceolate leaves. The formation of archegonia and antheridia is carried out in the tops of the stems of individuals, as a rule, growing side by side. In the antheridia, the formationbiflagellated spermatozoa, in archegonia - one immobile egg.
In the presence of a large amount of moisture (rain or heavy dew), fertilization begins. Water is essential, as spermatozoa swim up to the archegonium along it. When the zygote is formed, the sporophyte begins to develop from it. It is not viable in itself, like all plants included in the bryophyte department. The sporophyte is fed by the female gametophyte.
Sporogon box contains sporangium. There is the formation of haploid spores. Ripe, spores spill out. The wind blows them. If conditions are favorable, the spores will germinate and give rise to a protonema that looks like a green forked thread.
Sphagnum mosses
Sphagnum mosses (350 species) are another group of plants that make up the true moss class, mossy division. The general characteristics and significance of these mosses have a number of features. Sphagnum is the only genus of this subclass.
They are characterized by the absence of rhizoids, which is why the flow of water with dissolved minerals occurs directly to the cells of the leaf and stem. On the stem of the gametophyte there are whorls of branches, on which, in turn, leaves are located. They make up a rosette located at the top of the main axis.
Sphagnum moss leaves do not have a midrib. They contain two types of cells: living - assimilating (long and narrow, with chloroplasts), and dead (without protoplast, thickened on the walls, have pores). The second type of cells is also found in the stem. Suchthe anatomical structure of the stem and leaf of sphagnum allows it to absorb and retain such an amount of water that its mass can exceed the mass of the plant by 30 times. It is because of this that the soil on which sphagnum mosses grow gradually experiences excess moisture and becomes waterlogged.
So diverse is the bryophyte department. The reproduction of sphagnum mosses is typical, with the only difference from other representatives of the department that antheridia and archegonia can form not only on neighboring individuals, but also on the same plant.
The peculiarity of sphagnum mosses is the continuous growth of the stem at the top and the death of the lower part. But the dead parts do not rot completely, because waterlogged soil contains little oxygen, which is necessary for the development of soil microorganisms that decompose plant residues.
After a long period of time, a large amount of organic matter accumulates in the form of peat. Peat formation is a very slow process: 1 cm in about 10 years, 1 m in a thousand years.
Andrea mosses
Green and sphagnum mosses are the most numerous groups of plants in terms of the number of species that make up the mossy department. The general characteristics and significance of another group, despite its small number, make it possible to single it out as a separate taxonomic unit. The subclass Andrea mosses is represented by one family and one genus Andrea. Their distribution area is temperate and cold regions of both hemispheres. Grows in mountainous areason rocks and stones.
The gametophyte begins to develop even inside the spores. First, the cells begin to divide, and then the spore shells break. In single-layered leaves, the cells are homogeneous. The leaves grow apex for a long time, forming hygroscopic hairs. There are no vascular bundles in the stems.
Sporogony is represented by a box and haustoria. The box does not have a lid. When cracked, the spores get out through the cracks located between the 4 valves.
So, an extensive group of higher spore plants, second in number only to flowering ones, is the mossy department. The features of the structure and life of these representatives of the plant kingdom make it possible to call them amphibians, since they, as a rule, live on land (except for aquatic mosses), and can only reproduce in the presence of water.
