[Biology] Pteridophytes

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INTRODUCTION

  • 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

GENERAL CHARACTERISTICS

  • 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:

  • Psilopsida
  • Lycopsida
  • Sphenopsida
  • Pteropsida

PSILOPSIDA

  • 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

  • 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

  • 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

  • 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.

Learn Economic Importance of Pteridophytes in 3 minutes.

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:
  1. Microspores
  2. Megaspores

MICROSPORES

  • 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

  • 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.

ECONOMIC IMPORTANCE

  • 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.

REFERENCES

  • Arihant’s handbook of biology. Plant Kingdom. Page no: 24-42.
  • NCERT biology; textbook for class 11. Plant Kingdom. Page no: 46-62.
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