Pteridophyta: Characteristics, Classifications, Life Cycle

Pteridophyta, a kind of vascular plant, has nearly 12000 kinds of species. Pteridophyta are referred to as "cryptogams" because unlike most other members of the Plant Kingdom, Pteridophyta do not reproduce by seeds but rather through spores. Ferns, horsetails, and lycophytes come under Pteridophyta. 

Read Also: Five Kingdom Classification

Key Terms: Pteridophyta, Fern Pteridophyta, Primal Terrestrial Plants, Sporangia

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Characteristics of Pteridophyta

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Following are the key characteristics of Pteridophyta:

Primal Terrestrial Plants

It is an anticipation that life has originated in the waters and gradually adapted to dry land during millions of years of development. Similarly, Pteridophyta are primitively living terrestrial plants that have evolved.

Plant Body

A sporophyte is the primary plant body. It is further differentiated into stems, roots and leaves. 

1. Stems: The branches are mostly herbaceous, but some are woody. The branches could either be a monopodial stem or a dichotomous branching stem.
2. Roots: Roots are small and they accidentally grow along the rhizomes. 
3. Leaves: The leaves can be of three types like scale, small sessile and large petiolate compound.

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Vascular Plant

The vascular tissues are well developed in Pteridophyta. Xylem is made of tracheids and the phloem consists of sieve cells and phloem parenchyma. Although, the tissue lacks xylem vessels and phloem companion cells.

Sporangia in Sporophytes

Sporophytes have sporangia that are tended by sporophylls, which are leaf-like structures. To safeguard the delicate growth regions, the tip of the leaves curls inwards. Moreover, spores are produced inside the sporangia. Also, sporophylls may sometimes form compact structures known as cones or strobili. 

Formation of Spores

Spores are formed in the sporangia. The spores can be 

• Homosporous: Meaning only one type of spore is produced.
• Heterosporous: Meaning two kinds of spores are produced. 

Multicellular Sex Organs

Pteridophyta have multicellular sex organs. Antheridia are the male sex organ whereas archegonia are the female organ. The sexual organs are borne by the prothallus. A prothallus is a small gametophyte that develops after the germination of spores.

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Male and Female Reproductive System

Alternation of Generation

The Pteridophyta show an alternation of generation. It is proved by observing the presence of sporophyte and gametophyte generations in them. Meiosis is used by the dominant sporophyte to create spores. Mitosis produces gametes in the gametophyte generation. Pteridophytas and other plants have a life cycle called alternation of generations (also known as metagenesis).

Pteridophyta Diagram

Read More: Biodiversity and Conservation

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Pteridophyta: Classification

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Following is the classification of the Pteridophyta:

Psilopsida

• These are the earliest vascular plants to be discovered. The majority of them are now extinct.
• Psilotum and Tmesipteris are the only two surviving species left.
• It is a sporophyte with Rhizoids instead of roots.
• They have spirally organized lateral appendages such as scales or leaves.
• The leaves are mostly absent in psilopsida.
• Psilophyta or psilopsida is homosporous. 
• Examples are

1. Psilotum
2. Tmesipteris

Psilotum Diagram

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Lycopsida

• Lycopsida can be differentiated into roots, stems and leaves.
• It is most commonly known as club mosses. 
• It has microphyllous (small) leaves, with a single unbranched vein running across the midrib.
• Lycophyta or lycopsida are homosporous in the case of lycopodium or heterosporous in selaginella. 
• The axil of sporophylls consists of sporangia.
• The sporophylls are grouped in a strobili-like pattern.
• Examples are

1. Lycopodium
2. Selaginella

Lycopodium

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Sphenopsida

• It is also known as horsetail. 
• Sporangia seen in the axil of the plant body have nodes and internodes, just like higher vascular plants.
• Roots emerge from nodes of the underground rhizome, stem, and scaly leaves.
• Microphyllous leaves appear in whorls at each node.
• It is homosporous.
• An example is 

1. Equisetum

Equisetum Labelled Diagram

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Pteropsida

• Pteropsida is the largest group of Pteridophyta, with more than 9000 species.
• Plant body is differentiated into stems, leaves and roots.
• It is either homosporous or heterosporous.
• Antherozoids are multiflagellate.
• Leaves are advanced, being megaphyllous (large) and pinnately compound.
• Members of this class can be found in a variety of environments, including terrestrial, damp and aquatic. Moreover, some are epiphytes.
• Examples are

1. Pteris
2. Dryopteris
3. Adiantum

Adiantum

Read Important Chapter The Fundamental Unit of Life

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Life Cycle of Pteridophyta

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Pteridophyta show an alternation of generation. They have a similar life cycle to that of seed-bearing plants; unlike mosses and seed plants, Pteridophytas have distinct and free-living generations of haploid gametophyte and diploid sporophyte. Following is a brief life cycle of a Pteridophyta (in case of fern):

1. Pteridophyta reproduces through spores since they are flowerless and seedless.
2. In the beginning, spores are sent into the air. 
3. Spores grow into heart-shaped haploid gametophytes where both male and female sex organs are present.
4. Sex organs get active as soon as the young gametophyte matures. 
5. Antheridium (producing sperm) is the male reproductive organ in ferns whereas archegonium (producing eggs) is the female reproductive organ.
6. In case of fern reproduction, water is required for the sperm to flow and fertilize the egg. 
7. A fertilized egg, or zygote, develops roots, stems, and a new sporophyte through the process of mitosis (cell division). 

Life Cycle of Pteridophyta

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Things to Remember

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• Ultimately, Pteridophyta are primitive plants. 
• They are terrestrial plants that grow in wet, shaded environments. Some, like Selaginella lepidophylla (resurrection plant), survive in open, arid environments.
• Tribals eat Marsilea because it is a good source of starch.
• Ferns come in a variety of shapes and sizes, and they're used to treat various diseases. The herb Lycopodium clavatum is used to cure skin problems. Equisetum species are used as diuretics. Dryopteris is utilized in the production of anthelmintic drugs, which treats tapeworm infections.
• Ferns have been present on this planet for 360 million years. Moreover, ferns are found in abundance around us.

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