Kingdom Plantae – Pteridophytes

Introduction

The first terrestrial vascular plants are pteridophytes. They are classified under the group cryptogamae because they do not produce flowers and seeds. Pteridophytes have a transitional position between spermatophytes and bryophytes.

Pteridophytes

The word ‘pteridophytes’ is derived from the ‘pteron’ which is a Greek word that means feather and ‘python’ which means plants. Term pteridophyta was proposed by Haeckel The study of pteridophytes is known as pteridology. Pteridophytes are known as reptiles of the plant kingdom. In forests, ferns are found in abundance, these ferns are pteridophytes.  Some examples of pteridophytes are whisk fern, male fern etc.

Characteristics of Pteridophytes

In this section of the article we will discuss some key characteristics of pteridophytes.

• Pteridophytes are usually found in shady and moist places
• The main body of the plant has a well-differentiated stem, leaves and root is called a sporophyte
• Some of the species belonging to pteridophytes have small leaves known as microphylls. An example of pteridophytes having small leaves is selaginella
• Some pteridophytes have large leaves called megaphylls. An example of pteridophytes having large leaves is pterida
• Leaves may have spores on the underside. These leaves are known as sporophylls
• Sporophylls form compact structures called the strobili or cones
• Pteridophytes reproduce through spores as they are flowerless and seedless plants
• They are terrestrial vascular plants that have a well-developed vascular system with xylem and phloem. Xylem have four parts -tracheids, vessels ,xylem parenchyma, xylem and sclerenchyma in the angiosperm plant but the vessel is absent in pteridophyte

Phloem have four parts- sieve tube, companion cell, phloem parenchyma and phloem sclerenchyma in angiosperm but companion cell is absent in pteridophyte. The unique character of the life cycle of Pteridophyte is – Independent alternation of generation i.e sporophyte and gametophyte are separate to each other.

Examples of Pteridophytes

Following are some important examples of pteridophytes:

• • Whisk Fern

• Lycopodium

• Dicksonia

• Selaginella

• • Silver fern

• Equisetum

• Pteris

• Dryopteris

• Adiantum

The Life Cycle of Pteridophytes:

• • Pteridophytes display alternation of generations which is called metagenesis
  • The dominant sporophyte uses meiosis to create spores. Mitosis produces gametes in the gametophyte generation
  • The sporangia in the spore mother cells create the spores carried away by the wind. Gametophytes are formed when these spores germinate.In pteridophyta, the germination of spores is exosporic i.e. germination takes place outside the sporangia (in soil)
  • The gametophytes are multicellular, free-living and photosynthetic. They are known as prothallus. Due to their reliance on water, gametophytes prefer damp, moist and shady environments to thrive. As a result, pteridophyte development is restricted to only specific geographic locations
  • There is no relation between the main sporophytic plant and prothallus. Prothallus (gametophyte  plant) is made up of thallus and rhizoids. It is non vascular
  • Male sex organ is called antheridia, while female sex organ is called archegonium. The male gametes discharged are called antherozoids. Antherozoids can be transported to the archegonia only in the presence of water
  •  Fertilisation takes place by zooidogamy,Zooidogamy is a type of reproduction in which anterzoids swim in water for fertilisation with female gametes
  • A zygote is generated when the gametes fuse
  • After division, this zygote creates the sporophyte
  • Homosporous plants are those in which the spores of the plants are identical. Plants with two different types of spores are known as heterosporous. Megaspores and microspores germinate in these heterosporous plants, producing female and male gametophytes respectively
  • Type of sexual repro. in pteridophyta is oogamous

• Oogamous- fusion of gametes different in size , shape and behaviour
•  Their life cycle is diplo-haplonitc type

Classes of Pteridophytes / Classification of Pteridophytes

Oswald Tippo gave four classes of pteridophytes in 1942. Pteridophytes can be classified as –

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

Now we will discuss every class of pteridophytes in detail.

Psilopsida

Some of the important features of psilopsida are-

• This group has some of the most primitive vascular plants. Hence, most of its species are fossils now
• Some examples of psilopsida are psilotum and tmesipteris
• They do not have roots. They have an underground stem called a rhizome
• Rhizomes have small rhizoids that help absorb water and nutrients
• Their stem has dichotomous branches
• The sporophyte is homosporous
• They usually do not have leaves
• It grows as a saprophyte

Lycopsida

Some of the important features of lycopsids are-

• The plant body is divided into well-defined roots, stems and leaves
• Some examples of lycopsida are selaginella and lycopodium
• They are usually known as club moss
• They have dichotomous branches
• The sporophyte can be either homosporous or heterosporous
• They have small leaves

Sphenopsida

Some of the important features of sphenopsida are-

• They have only one living genus called equisetum
• Equisetum is homosporous
• An example of sphenopsida is equisetum
• Their branches are arranged in whorls
• Their stem contains distinct nodes and internodes
• They have photosynthetic gametophytes
• They have multiple flagella present on antherozoids
• They are commonly known as horsetails

Pteropsida

Some of the important features of Pteropsida are –

• This is the largest group of pteridophytes
• Some examples of pteropsida are dryopteris and pteris
• It has more than 9000 species
• Plants belonging to this group are highly evolved
• They are commonly known as a fern
• They have well-differentiated plant bodies
• They have spirally arranged leaves
• They have large leaves
• All plants belonging to this class are homosporous except aquatic ferns
• They have thick and short rhizomes
• Sporangia are present in clusters at the margins and tips of the leaves. These clusters are known as sori

Conclusion

Pteridophytes are one of the oldest families of plants in the plant kingdom. They are substantially older than angiosperms in terms of evolution. They were among the earliest “real” plants to adapt to land life. They are divided into four classes. Some of these plants have ornamental as well as medicinal value.