Characteristics of Pteridophytes:
- It originated in Silurian period of Palaeozoic Era
- It is the most primitive group. that flourished in Devonian and Carboniferous periods of Palaeozoic Era.
- They are more than forty four million old.
- The Pteridophytes include horsetails and ferns.
1. Habitat:
Evolutionary, they are the first terrestrial plants to possess vascular tissues – xylem and phloem. The pteridophytes are found in cool, damp, shady places though some may flourish well in sandy -soil conditions.
Some pteridophytes are found in other habitat also such as Azola, Salvinia and Marsilea found in aquatic condition. Isocitis found in marshy condition while Actinopteris found in desertic condition.
2. Habit:
In pteridophytes, the main plant body is a sporophyte which is differentiated into true root, stem and leaves but exceptionally in Psilotum roots and leaves are totally absent. Mostly perennial small herbs, shrub or trees, e.g., Pteris (Herb), osmunda regali, Tectoria (Shrub) and also phila(tree) but Azolla. Salvinia are annual and small herbs.
3. Primary roots are short lived which are substituted by adventitious roots.
4. The leaves in pteridophyta are scaly and small (microphylls) as in Equisetum, Lycopodium and Selciginellaov large (macrophylls) as in all ferns such as Adiantum. Pteris, Marsilea etc.
5. All body organs possess well -differentiated vascular tissues which made up of xylem and phloem. Vessels are absent in xylem and companion cells and sieve tubes are absent in phloem. Xylem is mainly made up of tracheids and phloem is mainly made up of sieve cellsbut exceptionally in some Pteridophytes vessels are present such as Equisetum, Selaginella and Marsilea.
6. Cambium is absent in Pteridophyta so no secondary growth in Pteridophyta (Exception: In Isocitis and Botrychium cambium present).
7. Pteridophtes also named as Vascular Cryptogamous because they are non floral plants with xylem and phloem. They are flowerless, seedless, spore producing vascular plants which have successfully invaded the land.
8. Reproduction:
Vegetative, asexual and sexual reproduction present in Pteridophyta. Vegetative and asexual reproduction is performed by sporophyte and sexual reproduction is performed by gametophyte.
9. Vegetative reproduction takes place by fragmentation and decay, Bulbils or Gemmae and by adventitious buds. Vegetative reproduction is not so common in Pteridophytes.
10. Asexual reproduction takes place by spores which are formed in sporangia on sporophyte. The sporangia are borne on leaf-like appendages called sporophylls in sporophyte stage. In some cases sporophylls may form distinct compact structures called strobili or cones (Selaginella, Equisetum). The sporangia produce spores (n) by meiosis in spore mother cells (2n). In majority of the pteridophytes all the spores are of similar kinds; such plants are called homosporous, eg.Equisetum, Pteris and other ferns but in 8-9 plants of genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous . Microspores develop in microsporangium while macrospore develops in megasporangium.
11. The spores (n) germinate to give rise to inconspicuous, small but multicellular, free-living, mostly photosynthetic thalloid gametophytes (n) called prothallus. in homosporous pteridophytes. Prothalus of main homosporous pteridophytes is heart shaped.In heterosporous pteridophyte. the megaspores germinate and give rise to female gametophytes and microspores germinate and giverise to male gametophytes.
The female gametophytes in these plants are retained on the parent sporophytes for variable periods. When Antheridia and Archegonia formed on same thallus then this condition is called monoecious but in some pteridophytes both the structure are formed on different thallus then it is called Dioecious. Sex organs are multicelluar which are enclosed with mutlicellular sterile jacket. In Antheridium flagellated male gamete Antherozoids are formed and in Archegonium non motile female gamete egg cell is formed.
Movement of antherozoids towards archegonium is chemotactic. Water is required for fertilization. The development of the zygote into young embryo takes place within the female gametophytes. This event is a precursor to the seed habit considered an important step in evolution. These gametophytes require cool, damp, shady places to grow because of this specific restricted requirement and the need of water for fertilisation, the spread of living pteridophytes is limited and restricted to narrow geographical regions. The gametophytes bear male and female sex organs called antheridia and archegonia, respectively.
Water is required for transfer of antherozoids(the male gametes) released from the antheridia, to the mouth of archegonium. Fusion of male gamete with the egg present in the archegonium result in the formation of zygote. Zygote there after produces a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes.
