Pteridophytes (Greek word- Pteron– feather, phyton– plant)
Pteridophytes are the first terrestrial plants (the most primitive cryptogamic land plants) that possess vascular tissue the Xylem and Phloem. The most common pteridophytes are horsetails and ferns and lower vascular plants. They are commonly called vascular cryptogams, snakes of plant kingdom or botanical snakes, or first tracheophytes.
Habitat: Found in cool, damp, shady places, some of them also found in sandy soil.
Uses– these are mostly used as ornamentals and for medicinal purposes.
Body organization: Main plant body is the sporophyte- (2n, diploid), differentiated into true root, stem, and leaves. well-differentiated vascular tissues are found.
In Xylem, the absence of true vessels, and phloem is without companion cells and sieve tubes. Secondary growth is absent in bryophytes.
In the vascular cryptogams, the ferns are the most advanced group.
Reproduction in Pteridophytes
Pteridophytes reproduce by both asexual and sexual means.
- In pteridophytes the leaves are small (microphylls) found in selaginella, or they may be large (macrophylls) as in ferns.
- Sporophytes bear Sporangia supported by leaf-like appendages known as sporophylls.
- In some pteridophytes like selaginella, equisetum the sporophylls found in a compact form called strobili or cones.
- Sporangia produce spores by the following meiosis in the spore mother cells.
- Two types of sporangium development found in pteridophytes:
- Leptosporangiate: in this type, the sporangium develops from a single superficial cell, e.g. Pteris, Dryopteris, Adiantum, and Salvinia.
- Eusporangiate: In this type, the sporangium develops from the group of cells. e.g. Silaginella,Equisetum, Psilotum.
- Haploid spores germinate a small, multicellular, free-living, and mostly photosynthetic thalloid gametophyte called prothallus.
- Cool, damp and shady areas are required for the growth of gametophytes.
- Need water for fertilization.
Sexual Reproduction in pteridophytes
Sexual reproduction by the development of gametophyte. Two types of gametophytes are found first endosporic i.e. inside the spore wall and exosporic i.e. outside the spore wall.
- The gametophyte bears male and female sex organs as antheridia and archegonia (a flask-shaped structure).
- Archegonia consists of a Basal swollen, embed portion called Venter enclosing egg and venter canal cell.
- The neck of archegonia comprises a neck canal cell (four-row) that may be uninucleate or binucleate. e.g of uninucleate- selaginella; and binucleate- ferns.
- Water is required for the transfer of antherozoids to the mouth of the archegonium. The antherozoids are released by the male gamete from antheridia to archegonium. Malic acid helps in it.
- The formation of the zygote takes place after the fusion of the male gamete with the egg.
- Zygote produces sporophyte that is the dominant phase of pteridophytes.
- Homosporous: All spores are or similar kinds, found in most pteridophytes.
- Heterosporous: plats in which micro and macrospores are found. for example- Selaginella
- Megaspore germinates female gametophyte and microspore germinate male gametophyte.
- Zygotes develop in young embryos (embryo stage for the short term) in female gametophytes. Seed habit is found as it and an important step in evolution.
The Gametophyte independent of sporophyte and short duration, but a new sporophyte is temporarily dependent upon gametophyte. As in bryophytes the gametophytic and Sporophytic phase alternative in it.
The pteridophytes show a haplo-diplontic life cycle. Heterologous alternation of generation, alternation of a dominant sporophyte. Heterospory leads to seed habits in plants.
Some Common Pteridophtes: Selaginella, whisk fern, Dicksonia, Lycopodium, Equisetum, Pteris, Adiantum.
Further Pteridophytes classified into four classes
- Psilopsida (Psilotum)
- Lycopsida (selaginella, Lycopodium)
- Sphenopsida (Equisetum)
- Pteropsida (Dryopteris, Pteris, Adiantum)
- These are the most primitive.
- Roots are absent.
- Having photosynthetic stem, dichotomously branched (two parts of stem- aerial and rhizomatous).
- Rhiziods are found and leaves are mostly absent.
- The sporophyte is found as homosporous synangium.
- common example:
- Living state: Psilotum and Tmesipteris.
- Fossil state: Cooksonia (Silurian), and Rhynia (Devonian).
- Commonly called club moss or spike mosses.
- They are primitive vascular plant, the body is well-differentiated with adventitious root, stem, rhizophores, and leaves.
- The homosporous or heterosporous sporophyte is found.
- Common Example: Selaginella (heterosporous), Lycopodium (homosporous).
- Commonly called horsetail.
- The plant body is differentiated, roots raised from nodes of the rhizome, stem, and scaly leaves found.
- Homosporous sporangia are borne on storbili.
- Common Example – Equisetum.
- These are commonly called fern.
- Plant body well differentiated with roots, stem, and leaves.
- Multicellular hairs ‘ramenta’ are present on young leaves and young stem. They work for protection.
- Sporophyte may be homosporous or heterosporous.
- Multiflagellate antherozoids are found.
- Common examples: Pteris (sun fern), Dryopteris (broke or male shield fern), Adiantum (walking fern and median hair fern).
Economic importance of Pteridophytes:
- They are used for medicinal purposes.
- They act as soil binders.
- From Dryopteris, an anthelmintic drug is obtained.
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