Pteridophytes

R.H Whittaker classified living organisms into five kingdoms based on cell structure, mode of nutrition, reproduction, and phylogenetic relationship. The five kingdoms are Monera, Protista, Fungi, Animalia, and Plantae.

Plant kingdoms have the following characteristics: 

• They are autotrophs, as they make their food by themselves. 
• They reproduce through both sexual and asexual modes (vegetative propagation). 
• They are non-motile. 
• They include multicellular and eukaryotic organisms
• The plant kingdom is further classified into Cryptogams and Phanerogams. 

Cryptogams are plants that reproduce by spores without seeds or flowers, known as cryptogams. Examples are ferns, lichens, algae, etc. They are further classified into Thallophyta, Bryophyta, and Pteridophyte. Phanerogams are seed-bearing plants. They are more advanced than cryptogams. They are further classified into Angiosperms and Gymnosperms. Here is a detailed explanation of Pteridophyta.

Pteridophyte

Characteristics of Pteridophyta

1. They are mostly grown as ornamentals.
2. They are commonly used for medical purposes and can also be used as soil binders.
3. The male sex organ is antheridia and the female organ is archegonia.
4.  Spores can be Homospores or Heterospores, they are formed in sporangia.
5. These pteridophytes plants possess both vascular tissues-xylem and phloem.
6. In the phloem, sieve tubes and companion cells are absent and, in the xylem, true vessels are absent.
7. They have well-differentiated structures such as leaves, stems, and roots as well as a vascular system.
8. They show true alteration of generation, as the saprophyte and the gametophyte generations are observed in pteridophytes.
9. Typical examples are ferns, Marsilea, Pteris, etc. Ferns encompass all living pteridophytes excluding lycopods and are vascular, unlike mosses and other bryophytes.

Classification 

In the recent past, the classification of pteridophytes has undergone vast changes due to the discovery of fossil plants. According to older taxonomists, vascular plants are classified into two divisions:

1. Pteridophyta: primitive vascular plants with the absence of seeds.
2. Spermatophyta: vascular plants with the presence of seeds.

Later on, they found a seed-bearing fossil plant, due to which the above classification became invalid. Then Sinnott introduced a new term known as Tracheophyte for a division that possesses sporophytes with well-developed vascular tissues.

According to Arthur J. Eames, Tracheophyte is classified into four subdivisions-

1. Psilopsida
2. Lycopsida
3. Sphenopsida
4. Pteropsida 

Psilopsida

• Includes living and fossil plants.
• The body organization of plants is very simple.
• Members are this division is sporophytic.
• Plant bodies can be differentiated into a subterranean rhizome and an erect aerial portion.
• Roots are absent in these plants.
• Includes 2 classes:
  • Psilotopsida
  • Psilopsida

Lycopsida

• Includes living and fossil plants.
• Members are this division is sporophytic.
• Plant bodies can be differentiated into roots, leaves, and stems.
• Plants have small and simple with a single mid-vein leaf.
• Leaf gaps are absent in these plants.
• Includes 2 classes:
  • Eligulopsida
  • Ligulopsida

Sphenopsida

• Includes both fossil and living plants.
• The plant body is sporophytic.
• Plant bodies can be differentiated into roots, leaves, and stems.
• The stem of the plant is divisible into nodes and internodes.
• The leaves of the plants are small, thin, and scaly brown.
• The embryo is without a suspensor.
• Includes 2 classes:
  • Sphenophyllopsida
  • Calamopsida

Pteropsida

• Includes plants that are commonly known as ferns.
• Some members of this have very small trees, while some have tall trees.
• Leaves may be simple or compound, but they are large in shape.
• An embryo may or may not have a suspensor.
• Vegetative reproduction can be done through fragmentation, stem tubers, adventitious buds, or apogamy.
• Includes 4 classes
  • Peimofilicopsida 
  • Eusporangiopsida
  • Protoleptosporangiopsida
  • Leptosporangiopsida

Sub-division	Psilopsida		Lycopsida		Sphenopsida		Pteropsida
Classes	Psilotopsida	Psilopsida	Eligulopsida	Ligulopsida	Sphenophyllopsida	Calamopsida	Peimofilicopsida	Eusporangiopsida	Protoleptosporangiopsida	Leptosporangiopsida
Orders	Psilophytales	Psilotales	Lycopodiales	1.Selaginellales 2.Lepidodendronales 3.Isoetales 4.Pleuromeales	Sphenophyllales	1.Calamitales 2.Hyeniales 3.Equisetales	1.Cladoxyales 2.Coenopteridales	1.Ophioglossales 2.Marattiales	Osmundales	1.Filicales 2.Marsileales 3.Salvineales

Economic Importance 

1. They are grown as ornamental plants for their delicate and graceful leaves.
2. Pteridophytes are grown as a soil-binding agent, as they bind the soil even along hill slopes.
3. Equisetum stems have been used for metal polishing and scouring (cleaning of cutlery). Scouring rushes are another name for Equisetum species.
4. Anabaena azollae, a cyanobacterium that fixes nitrogen, coexists symbiotically with the water fern Azolla. It is immunized against paddy fields that act as biological fertilizers.
5. Pteridophytes serve as a valuable source of food for animals, just like other plants. A water fern called Marsilea produces starch in its sporocarps, which is consumed by the tribal peoples.
6. Dryopteris rhizomes are used to make an anthelmintic medication (Male Shield Fern).

Life Cycle of Pteridophytes

In contrast to mosses and seed plants, Pteridophytes contain distinct and free-living generations of haploid gametophyte and diploid sporophyte, which have a life cycle comparable to that of seed-bearing plants. Here is a brief description of a Pteridophyta’s life cycle (in the case of ferns):

• Since Pteridophyta does not produce seeds or flowers, they reproduce by spores.
• Spores are initially released into the atmosphere.
• Spores develop into haploid gametophytes with both male and female sex organs that are heart-shaped.
• As soon as the immature gametophyte grows, the sex organs become functional.
• In ferns, the male reproductive organ is called an antheridium, which produces sperm, while the female reproductive organ is called an archegonium, which has eggs.
• Water is necessary for the sperm to flow and fertilize the egg in the case of fern reproduction.
• Through the process of mitosis, a fertilized egg, or zygote, creates new roots, stems, and sporophytes (cell division).

Similarities in the Sexual Reproduction of Ferns and Moss

• The mode of sexual reproduction is oogamous as non-motile female gametes are fertilized with motile gametes.
• Female sex organs are flask-shaped with a tubular neck and a swollen basal venter.
• Requirement of external source water for sperm to reach archegonia.
• Shows the true alternation of generations.

Dissimilarities in the Sexual Reproduction of Ferns and Moss

• Ferns have vascular tissues, moss doesn’t.
• Ferns are sporophyte dominant and mosses are gametophyte.
• Ferns have both male and female parts on the same plant, mosses have separate parts.

FAQs on Pteridophytes

Question 1: Write the classification of the plant kingdom.

Answer:

Plant kingdom is further classified into:

1. Cryptogams
2. Phanerogams.

Cryptogams are plants that reproduce by spores without seeds or flowers are known as cryptogams. Examples are ferns, lichens, algae, etc. They are further classified into Thallophyta, Bryophyta and Pteridophyta. 

Phanerogams are seed-bearing plants. They are more advanced than cryptogams. They are further classified into Angiosperms and Gymnosperms.

Question 2: Write the male and female organs in Pteridophyta.

Answer:

The male sex organ is antheridia and the female organ is archegonia.

Question 3: What are Tracheophyta and its classification according to Arthur J. Eames?

Answer:

Tracheophyta is the one that possesses sporophytes with well-developed vascular tissues.

According to Arthur J. Eames, Tracheophyta is classified into four sub-division-

1. Psilopsida
2. Lycopsida
3. Sphenopsida
4. Pteropsida 

Question 4: Define ferns and mention the similarities and dissimilarities with mosses.

Answer:

Ferns encompass all living pteridophytes excluding lycopods and are vascular, unlike mosses and other bryophytes.

Similarities:

• The mode of sexual reproduction is oogamous.
• Shows the true alternation of generations.

Dissimilarities:

• Ferns have vascular tissues, moss doesn’t.
• Ferns have both male and female parts on the same plant, mosses have separate parts.

Question 5: Write the characteristics of Sphenopsida.

Answer:

Sphenopsida-

• Includes both fossil and living plants.
• The plant body is sporophytic.Plant bodies can be differentiated into roots, leaves, and stems.
• The stem of the plant is divisible into nodes and internodes.