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Vascular plants that disperse spores and have xylem and phloem in them are termed Pteridophytes. They are commonly referred to as “cryptogams,” indicating that their mechanisms of reproduction are hidden because they do not produce blooms or seeds. They include ferns, horsetails and lycophytes. Pteridophyta is no longer a commonly recognised taxon, although the term pteridophyte, as well as pteridology or pteridologist as a discipline and its practitioner, are still used in everyday speech.
Haeckel was the first one to coin the word Pteridophyta, whereas Cryptogamia and Phanerogamia were established by Eichler in 1883 to split the plant kingdom. Thallophyta was added to the Cryptogamia division. Bryophyta and Pteridophyta are two groups of plants. Bryophyta and Pteridophyta were included in the Embryophyta by Engler in 1909.
The taxonomy of Pteridophytes has changed dramatically in recent years as a result of the finding of ancient plants. Older taxonomists separated vascular plants into two groups: Pteridophyta (non-seedless vascular plants) and Spermatophyta (seedless vascular plants)
Classification of Pteridophytes
1 – Psilopsida
The subdivision Psilopsida / Division Psilophyta includes both living (example, Psilotum) and fossil flora (example, Rhynia).
Their characteristics are:
There are no roots.
The members’ plant bodies are organised in a very simple way. A subterranean rhizome, as well as an erect aerial part, are distinguishable.
Rhizome has tufts of unicellular Rhizozoids
The aerial section is sparsely branched or heavily branched. Branches are frequently dichotomous.
The aerial axis could be without leaves or contain scaly appendages or huge foliage leaves.
The vascular tissue is primitive, consisting of a basic cylinder protostele containing annular/spiral tracheids.
The sexual organs have the shape of sporangia, which are sac-like structures.
Sporangia bloom at the tops of aerial shoots, which are either solitary or in groups and are terminal.
Sporangia are homosporous, indicating they always produce the same sort of spores.
The gametophyte is only known in the extant genera Psilotum & Tmesipteris and is unidentified in the Psilophytales.
The gametophyte is underground, cylindrical or branching, and colourless.
The prothallus has a portion of the sex organs embedded in it.
Antherozoids in Psilotales are multiciliated.
2 – Lycopsida
It comprises both fossil and extant Pteridophytes (e.g., Lepidodendron) Its characteristics are:
The leaves are microphyllous (tiny), simple, and have a single midvein.
They’re frequently arranged in spirals, sometimes in opposite directions and sometimes in whorls.
The leaves are ligulate in some circumstances (e.g., Selaginella, Isoetes). Each leaf’s ligule can be found at the base.
Vascular tissue can assume the shape of plectostele or siphonostele in some cases.
There are no leaf gaps.
Sporangia form on the axial surface of leaves and are rather big (sporophylls).
Sporophylls produce strobilus when they are loosely organised.
Some members (e.g., Lycopodium) are homosporous, while some are heterosporous (example., Selaginella).
Biflagellate or multiflagellate antherozoids
Germination of spores produces gametophytes in the manner of prothalli.
Endoscopic gametophytes are found in heterosporous forms, whereas exoscopic gametophytes are found in homosporous forms.
3 – Sphenopsida
It is a phylum of the Sphenopsidae family.
It comprises both fossil and modern plants ( for example, Calamophyton, Sphenophyllum). Equisetum is the only living genus, and there are 18 extinct forms.
These Pteridophytes emerged during the Palaeozoic era’s Carboniferous phase.
The sporophytic plant body is divided into three parts: root, stem, and leaves.
In the majority of forms, the stem is tall, jointed, articulated, and ribbed, meaning it has ridges and grooves.
On the nodes of the aerial branches, thin, tiny, scaly brown leaves are grouped in transverse whorls.
Out from the axil of a scaly leaf, branches grow in whorls.
As the foliar leaflets are decreased to scales, the stem absorbs the photosynthetic activity and turns green.
The stem has a medullated protostele or a solid protostele
In certain extinct forms, secondary thickenings have been found (e.g., Sphenophyllum).
Sporangia grow in whorls at the tip of fertile branches, making a tight cone.
Although living classification organisms are homosporous, certain fossil forms were heterosporous (for example Catamites).
Spores germinate to produce gametophytes, which can be monoecious and dioecious.
Antherozoids are multiflagellate and huge.
The embryo lacks a suspensor.
4 – Pteropsida
This sub-division contains the plants often referred to as “ferns.” There are roughly 300 genera and over 10,000 species in it.
They can be found in a variety of environments and the majority of ferns are terrestrial, preferring wet, shaded environments. Some are xerophytic, epiphytic, halophytic or climbing.
Certain members are little, while others are as tall as trees (e.g., Angiopteris).
The majority of members (except for a few tree ferns, such as Angiopteris) have a short and fat rhizome. The rhizome might be crawling, upright, and above ground.
Fronds are large, simple or compound leaves that are classified as fronds.
The Young fronds are wrapped in a circle.
Some leaf groups are exstipulate (e.g., Filicales), whereas others are stipulate.
The vascular cylinder can range from a simple proposed to a complex siphonostele.
Plants reproduce by fragmentation, stem tubers, adventitious buds, or apogamy.
Conclusion
In this article, we’ve discussed pteridophytes, their characteristics and classification. Pteridophytes are free-sporing vascular plants that go through gametophyte and sporophyte phases in their life cycle. Ferns, horsetails, and lycophytes are among them. Although Haeckel was the first to invent the term Pteridophyta, it is no longer a widely accepted taxon. The four groups/sub-divisions of Pteridophytes are Psilopsida, Lycopsidae, Sphenopsida and Pteropsida, whose characteristics are mentioned in the article.
