To the pteridophytesalso called seedless vascular plants, are a group of plants in which the presence of xylem and phloem (conducting vessels) and the absence of seeds are observed, a characteristic that appears only in gymnosperms. The oldest fossils of plants with conducting vessels are from around 425 million years ago. In Brazil are found more than 1000 species of pteridophytes, being possible to mention as representatives of this group the ferns and the horsetails.
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Pteridophytes are plants that have the xylem and phloem as fabrics specializing in conduction. The emergence of these tissues was possible thanks to the emergence of ligninwhich guarantees resistance xylem elements and sclerenchyma cells. The resistance acquired by these plants was an essential step for them to become larger in size than bryophytes.
In these plants we observed a alternation of generationsin which the sporophyte (spore-producing stage of the life cycle) 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 the latter group, the dominant generation is the gametophyte (gamete-producing phase of the life cycle).
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In these plants, the presence of roots, stalk It is real leaves. The roots act in fixing the plant to the substrate and in the removal of nutrients and water from the soil. The stem acts as a structure that ensures the support of the leaves. The leaves are related to the realization of photosynthesis.
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In these plants, the water need so that the fertilization occur. This is due to the fact that male gametes are flagellated and need swim to the female gametophyte to fertilize the oosphere (female gamete). Due to this characteristic, we find the plants of the pteridophytes group, mainly, in wet places. In these plants, the presence of pollen grains, seeds, flowers or fruits is not observed.
A Selaginella It is a genus of plants in the group of vascular seedless plants.
Pteridophytes are observed in a big variety habitat, found in forest environments and even in dry areas. Nonetheless, the vast majority of species are found in regions where there is a higher moisture in the soil.
→ Life cycle
There are different types of pteridophytes, so there are different life cycles in this group of plants. In the following, we describe the life cycle of a homosporous ferna very characteristic plant of the group of seedless vascular plants.
Look at the sori on the underside of a fern leaf.
The vast majority of pteridophytes are characterized by being homosporated, that is, they only have a type of sporangiumwhich is capable of producing only a type of sporewhich develops into a bisexual gametophyte. A small plot of seedless vascular plants is heterosporous.
In this type of plant, it is observed two types of sporangiawhich produce two types of spores. megasporangia are responsible for producing megaspores, which form the female gametophytesIt is microsporangia produce microspores, which develop male gametophytes. In Selaginellafor example, heterospory is observed.
In the adult fernsthere are leaves that, on their anterior side, have serumsthat are sporangia clusters. Inside the serums, the meiosis spores. When the serum releases the fern spores, they fall into the environment and germinate, when the conditions are right, giving rise to a gametophyte.
Observe the main stages of the pteridophyte life cycle.
The gametophytes are green It is 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 archegoniums It is antheridia. Archegonia are responsible for producing the oosphere, while antheridia produce antherozoids.
usually the archegonium and the gametophyte antheridium of the fern mature in different times, and therefore fertilization usually involves gametes produced in different gametophytes. The antherozoid will swim to the egg and fertilize it. A zygote will form, which will divide and, over time, differentiate into an adult sporophyte. As soon as the sporophyte attaches itself to the soil, through its roots, the gametophyte is disintegrated.
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Pteridophytes are currently classified into two phyla:
Lycopodiophyta: In this group we find Lycopodium, Selaginella It is Isoetes.
Monilophyta: In this group we find ferns and Equisetum.
O Equisetum is part of the phylum Monilophyta.
Pteridophytes are plants that are important economical and also ecological. Like all plants, pteridophytes are producing organismstherefore being the base of some food chains. In addition, the ancestors of current 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 turned into charcoal, a product of great economic value.
Know more: geological eras
In addition to coal, we cannot fail to mention that some current species have also been heavily exploited economically, such as ferna species of fern that reaches about five meters high. This plant was used in the manufacture of tree fern, a type of vase. Currently, tree fern can no longer be manufactured, as the plant is in endangered species list.
→ Difference between bryophytes and pteridophytes
Bryophytes and pteridophytes are relatively simple plants that have some similarities as well as some differences. Below is a comparison chart between the two:
Reliance on water for reproduction
Enduring phase of the life cycle
mosses and liverworts
Ferns and Horsetails
By Ma. Vanessa Sardinha dos Santos