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Bryophytes (from Greek bryon: 'moss'; and phyton: 'plant') are small plants, usually a few inches tall, that live preferentially in humid and shady places.
The body of moss is basically made up of three parts or structures:
- rhizoids - filaments that attach the plant to the environment in which it lives and absorb the water and mineral salts available in that environment;
- cocoon - small stem from where the phylloids depart;
- phyloids chlorophyll structures capable of photosynthesis.
These structures are called rhizoids, kauloids and phylloids because they do not have the same organization of roots, stems and leaves as the other plant groups (from the pteridophytes). They lack, for example, conductive vessels specializing in the transport of nutrients such as water. In the organization of the true roots, stems and leaves, there are nutrient-carrying vessels.
Because absence of nutrient-carrying vessels, the water absorbed from the environment and is transported in these plants from cell to cell throughout the body of the plant. This type of transport is relatively slow and limits the development of large plants. Thus, bryophytes are always small, short.
Follow the reasoning: If a large terrestrial plant had no conductive vessels, it would take a long time for the water to reach the leaves. In this case, especially on hot days - when the leaves usually sweat a lot and lose a great deal of water to the environment - they would become dehydrated (dry out) and the plant would die. Thus, the entire tall plant has conductive vessels.
But not all plants that have conductive vessels are tall; grass, for example, has conductive vessels and is small in size. However, one thing is certain: if the terrestrial plant has no conductive vessels, it will be small and live in preferably damp and shady environments.
Mosses and liverworts are the main representatives of bryophytes. The name hepatic comes from the Greek hepathoswhich means 'liver'; These plants are so named because their bodies resemble the shape of a liver.
Mosses are standing plants; the liverweeds grow "lying" in the soil. Some bryophytes live in freshwater, but no marine species are known.
Reproduction of bryophytes
To explain how bryophytes reproduce, we will model mimoso moss. Observe the scheme below.
The green mosses that we see in moist soil, for example, are sexed plants which represent the phase called gametophyte, that is, the gamete producing phase.
In bryophytes, gametophytes generally have separate sexes. At certain times, gametophytes produce a small structure, usually in the apical region - where the phylloids end. There gametes are produced. Male gametophytes produce mobile gametes with flagella: the anterozoids. Female gametophytes, on the other hand, produce immobile gametes, called oospheres. Once produced in the male plant, the anterozoids they can be taken to a female plant with falling and splashing rainwater.
In the female plant, anterozoids swim toward the oosphere; From the union between an anterozoid and an oosphere arises the zygote, which develops and forms an embryo over the female plant. The embryo then develops into an asexual phase called sporophyte, that is, the spore producing phase.
In the sporophyte it has a rod and a capsule. Inside capsule the spores form. When mature, the spores are released and can germinate in moist soil. Each spore can then develop into a new green moss - the sexual phase called gametophyte.
As you can see, bryophytes depend on water for reproduction, as anterozoids need it to move and reach the oosphere.
The chlorophyllated green moss constitutes, as we have seen, the phase called gametophyte, considered lasting because the moss stays alive after the production of gametes. Already the phase called sporophyte has no chlorophyll; It is nourished by the female plant on which it grows. The sporophyte is considered a transient phase because it dies shortly after producing spores.