- The term Pteridophyte is derived from two words ‘Pteron’ meaning “feather” and ‘phyton’ meaning “plant”.
- Pteridophytes are the first evolved plant group with a vascular tissue system for the conduction of water and food materials.
- Members of pteridophytes are seedless, vascular cryptograms.
- Being vascular plants, Pteridophytes are known as tracheophytes
- Pteridophytes are the most primitive living vascular plants and mostly inhabit cool, damp, and shady places.
- Pteridophytes are vascular plants, that contain specialized vascular tissues but lack xylem vessels and phloem companion cells.
- The plant body is differentiated into true roots, stems, and leaves.
- They show alternation of generation with diploid sporophytes being the dominant phase.
- spores are produced in a structure called sporangia.
- Plants may be homosporous (one type of spores are produced) or heterosporous (different types of spores are produced).
- Sporangia are borne on leaves and are termed as sporophylls.
- Spores grow into a multi-cellular gametophytic body called prothallus.
- Prothallus is independent and chlorophyllous.
- The male reproductive organ is antheridium while the female reproductive organ is archegonium.
- Reproductive organs are multicellular and jacketed.
- The embryo develops in situ after fertilization.
- Water is essential for their fertilization as male reproductive units are flagellated and motile.
- The sporophyte remains attached to the gametophyte till the development of the root.
CLASSIFICATION OF PTERIDOPHYTES
Pteridophytes are categorized into four major classes:
- The plants in this group have a rootless sporophyte body that differentiates into a subterranean rhizome and an aerial erect shoot.
- Branching is dichotomous in both subterranean rhizome and aerial shoot.
- Rhizoids emerge from the rhizome and function to absorb water and nutrients from the soil.
- Leaves are usually absent in psilopsida.
- Spores are of equal sizes and shapes and are homosporous.
- Lycopsida is also known as club mosses
- The sporophyte plant body is differentiated into true stems, leaves, and roots and is dichotomously branched.
- Leaves are present and are commonly small and microphyllous.
- The spores may be either homosporous or heterosporous.
- The spores develop into independent gametophytes.
- Sphenopsida is also known as horsetails.
- Most of the members are homosporous, in which sporangia are borne on strobili.
- The plant body is well-differentiated, with roots arising from nodes of the underground rhizome, stem, and scaly leaves.
- Pteropsida is also known as ferns.
- The plant boy is highly differentiated and distinguished into roots, stem, and spirally arranged leaves.
- Most of the members grow in moist and shaded habitats, either epiphytic or terrestrial however, a few are aquatics.
- Many ferns are homosporous, but a few aquatic members are heterosporous.
LIFE CYCLE OF PTERIOPHYTES
- Pteridophytes show alternation of generation with the sporophyte phase being the dominant phase.
- Spores are produced via meiosis inside the sporangia. Sporangia are borne on the sporophyte plant body, subtended by leaf-like appendages called sporophylls.
- The Spores upon germination, give rise to a multicellular gametophyte called prothallus.
- Prothallus is a free-living, photosynthetic, thalloid structure that inhabits cool, damp, and shady areas.
- The prothallus bears male and female sexual organs known as antheridia and archegonia respectively.
- The antheridium bears male gametes (antherozoids) whereas the archegonium bears female gametes (egg).
- Water is required for the transfer of antherozoids from the antheridium to the archegonium.
- The fusion of antherozoid with the egg results in zygote formation.
- Zygote further develops to give rise to the multicellular, well-differentiated sporophyte.
HETEROSPORY IN PTERIDOPHYTES
- Heterospory is a condition in which more than one type of spores is produced in a single plant.
- These two types of spores differ in their formation, structure, functionality, and sexuality.
- In pteridophytes, there are two types of spores:
- These are small-sized spores which are produced in large numbers inside the structure called microsporangium
- These are male spores which produce male gametophyte upon germination
- Megaspores are larger spores which are produced in limited numbers inside the microsporangium
- These are female spores that give rise to female gametophytes upon germination.
- Pteridophytes are vital in the food chain and act as a source of nutrition and fiber for animals.
- Pteridophytes bind the soil, even along hilly slopes. In this way, the soil is protected from erosion.
- Equisetum stems have been used in cleaning of utensils and polishing of metals
- An anthelmintic drug is obtained from the rhizomes of Dryopteris (Male Shield Fern).
- Ferns are used as ornamental plants because of their delicate and graceful leaves.
- Arihant’s handbook of biology. Plant Kingdom. Page no: 24-42.
- NCERT biology; textbook for class 11. Plant Kingdom. Page no: 46-62.