Pteridophytes
- They include horsetails and ferns.
- They are found in cool, damp, shady places. Some flourish well in sandy-soil conditions.
- Evolutionarily, they are the first terrestrial plants to possess vascular tissues (xylem & phloem).
- In bryophytes, the dominant phase in the life cycle is the gametophyte. In pteridophytes, the dominant phase (main plant body) is a sporophyte. It is differentiated to true root, stem & leaves. These organs have well-differentiated vascular tissues.
- The leaves in pteridophyta are small (microphylls) as in Selaginella or large (macrophylls) as in ferns.
Economic importance:
- They are used for medicinal purposes and as soil-binders and ornamentals.
Reproduction:
- The sporophytes bear sporangia that are subtended by leaf-like appendages called sporophylls. In some cases, sporophylls may form distinct compact structures called strobili or cones (E.g. Selaginella, Equisetum).
- Sporangia produce spores by meiosis in spore mother cells.
- The spores germinate to give inconspicuous, small, multicellular, free-living, mostly photosynthetic thalloid gametophytes called prothallus.
- Prothallus requires cool, damp, shady places to grow. Also, it needs water for fertilization. So, the spread of pteridophytes is limited and restricted to narrow geographical regions.
- The gametophytes (prothallus) bear male and female sex organs called antheridia and archegonia, respectively.
- Water is needed for transfer of antherozoids (male gametes from antheridia) to the mouth of archegonium.
- Antherozoid fuses with the egg in the archegonium to form zygote. Zygote develops to a multicellular well-differentiated sporophyte.
- Most of the pteridophytes produce similar kinds of spores (homosporous plants). Others produce two kinds of spores, macro (mega) & micro spores. They are heterosporous. E.g. Selaginella & Salvinia.
- The megaspores & microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes are retained on the parent sporophytes for variable periods.
- Within female gametophytes, zygotes develop into young embryos. This event is a precursor to the seed habit. It is considered as an important step in evolution.
- The pteridophytes have 4 classes:
- Psilopsida: E.g. Psilotum
- Lycopsida: E.g. Selaginella, Lycopodium
- Sphenopsida: E.g. Equisetum
- Pteropsida: E.g. Dryopteris, Pteris, Adiantum
