At pteridophytes, also called seedless vascular plants, are a group of plants in which the presence of xylem and phloem (conducting vessels) and the absence of seeds, a characteristic that appears only in the gymnosperms. You fossils oldest plants with conducting pots are about 425 million years ago. In Brazil are found more than 1000 species of pteridophytes, and it is possible to cite as representatives of this group the ferns and the horsetails.
→ Features
Pteridophytes are plants that have the xylem and the phloem like specialized tissues in driving. The emergence of these tissues was possible thanks to the emergence of lignin, which guarantees resistance to the xylem elements and sclerenchyma cells. The resistance acquired by these plants was an essential step for them to become bigger in size than the bryophytes.
In these plants we observe a alternation of generations, in which the sporophyte (spore-producing life cycle stage) stands out for being the dominant generation. The sporophyte in these groups is
bigger and also more complex than the gametophyte. This characteristic also differentiates them from bryophytes, since, in this last group, the dominant generation is the gametophyte (phase of the gamete-producing life cycle).Do not stop now... There's more after the advertising ;)
In these plants, the presence of roots, stalkandsheets true. The roots act in fixing the plant to the substrate and in removing nutrients and water from the soil. The stem acts as a structure that guarantees the support of the leaves. The sheets, on the other hand, are related to the realization of the photosynthesis.
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In these plants, the need for water for the fertilizationoccur. This is due to the fact that the gametes male are flagellated and need swim to the female gametophyte to fertilize the oosphere (female gamete). Due to this characteristic, we find plants from the pteridophyte group, mainly in wet places. In these plants, the presence of pollen grain, seeds, flowers or fruits.
THE Selaginella is a genus of plants in the group of seedless vascular plants.
→ Habitat
Pteridophytes are observed in a big variety in habitat, being found in forest environments and even in dry areas. However, the vast majority of species are found in regions where there is a greater soil moisture.
→ Life cycle
There are different types of pteridophytes, so there are different life cycles in this group of plants. We will describe below the life cycle of a homosporous fern, a plant quite characteristic of the group of vascular seedless plants.
Note the serums on the underside of a fern leaf.
The vast majority of pteridophytes are characterized by being homosporous, that is, they only have a kind of sporangium, which is capable of producing only a kind of spore, which develops into a bisexual gametophyte. A small portion of seedless vascular plants is heterosporad.
In this type of plant, it is observed two types of sporangia, which produce two types of spores. Megasporangia are responsible for producing megaspores, which form the female gametophytes, and microsporangia produce microspores, which develop the male gametophytes. In Selaginella, for example, heterosporia is observed.
In the adult ferns, there are leaves that, on their front side, have serums, that are sporangia sets. Inside the serums, the meiosis spores. When the serum releases the fern spores, they fall into the environment and germinate, when under suitable conditions, giving rise to a gametophyte.
Observe the main steps in the life cycle of pteridophytes.
The gametophytes are green and nutritionally independent of the sporophytes. They look like a heart and have small filaments called rhizoids, which are directed to the substrate. Bisexual gametophytes have archegons and antheridia. Archegons are responsible for producing the oosphere, while antherids produce anterozoids.
Usually the archegon it's the gametophyte antheridium of the fern mature in different times, and therefore fertilization usually involves gametes produced in different gametophytes. The anterozoid will swim to the oosphere and fertilize it. The formation of the zygote, which will divide and, over time, differentiate into an adult sporophyte. As soon as the sporophyte attaches itself to the ground through its roots, the gametophyte is disintegrated.
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→ Classification
Pteridophytes are currently classified into two filaments:
Lycopodiophyta: In this group we find Lycopodium, Selaginella and Isoetes.
Monilophyta: In this group we find ferns and Equisetum.
O Equisetum is part of the phylum monilophyta.
→ Importance
Pteridophytes are plants that are important economical and also ecological. Like all plants, pteridophytes are producer bodies, being, therefore, the base of some food chains. In addition, the ancestors of today's pteridophytes formed the first large forests, which contributed to the reduction of carbon dioxide levels in the atmosphere, in the Carboniferous period. The seedless vascular plants that formed the first forests later became coal, being this product of great economic value.
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In addition to coal, we cannot fail to mention that some current species were also economically exploited, which is the case of fern, a species of fern that reaches around five meters high. This plant was used in the manufacture of tree fern, a type of vase. Currently, tree fern fiber can no longer be manufactured, as the plant is in the endangered species list.
→ Difference between bryophytes and pteridophytes
Bryophytes and pteridophytes are relatively simple plants that have some similarities and also some differences. See, below, a comparative chart between them:
FEATURES |
BRYOPHYTES |
PTERIDOPHYTES |
conductive vessels |
absent |
gifts |
Source |
Absent |
Gift |
Stalk |
Absent |
Gift |
Sheets |
absent |
gifts |
seeds |
absent |
absent |
Flowers |
absent |
absent |
fruits |
absent |
absent |
Dependence on water for reproduction |
Gift |
Gift |
lasting phase of the life cycle |
Gametophyte |
Sporophyte |
Examples |
Mosses and liverworts |
Ferns and Horsetails |
By Ma. Vanessa Sardinha dos Santos
