What are Pteridophytes?

They are the first land plants with vascular tissues (xylem and phloem). These vascular plants are classified as vascular cryptogams because they do not contain flowers or seeds. These plants are the most common and visible group of land plants, accounting for more than 90% of all vegetation on the planet.

Pteridophytes

Pteridophyta is one of the Plant Kingdom's oldest families. They are much older than angiosperms in terms of evolution. They were among the first "true" plants to adapt to land life.

True roots, branches, and leaves are well-differentiated in the plant body of these species.

For hundreds of millions of years, the landscape was dominated by plants that looked like ferns before flowering plants appeared. Pteridophytes share many traits with their forefathers. Unlike most other Plant Kingdom members, pteridophytes do not replicate through seeds but rather through spores.

Pteridophytes, like bryophytes, are seedless, flowerless plants that rely on the development of spores for propagation. They are autotrophs, meaning they produce their food by photosynthesis. On the other hand, pteridophytes differ from bryophytes in that they are vascular plants with structures that carry water from roots to stems and leaves. Ferns and closely related species, unlike mosses, are homosporous, meaning they have only one type of spore.

Evolution of Pteridophytes

The Devonian stage, which lasted from about 416 to 359 million years ago during the Paleozoic Era, has a fossil record for the Pteridophyte group. There are approximately 13,000 species today, divided into 35 plant families and 568 genera. Many epiphytes, though not all, are also pteridophytes. Epiphytes live on other plants in tropical habitats and get their water from the air or rainfall. Spike moss (not a true moss), quillworts, and club moss are examples of common pteridophytes (also not true moss). A variety of pteridophytes, including Salvinia, water ferns, water velvet, and water sprites, are also aquatic.

Features of Pteridophytes

1. They are the first land plants on earth: It is thought that life started in the oceans and gradually adapted to dry land over millions of years of evolution. The pteridophytes were among the first plants to exist on land truly.
2. They are seedless vascular plants: Pteridophytes do not have seeds and reproduce by spores. Vascular tissues are present, but xylem vessels and phloem companion cells are absent.
3. The plant body of these organisms has true roots, stems, and leaves: The plant body is divided into the stem, roots, and leaves.
4. Spores develop in sporangia: The structures in which spores are produced are known as sporangium. They are both homosporous (producing only one type of spore) and heterosporous (producing several types of spores) (meaning: two kinds of spores are produced.)
5. In these plants, sporangia are produced in groups on sporophylls: Sporophylls are leaves that have sporangia on them. To cover the fragile growing sections, the tip of the leaves curl inwards.
6. They have multicellular sex organs: Male sex organs are referred to as antheridia, while female sex organs are referred to as archegonia.
7. These plants show true alternations of generation: In pteridophytes, the sporophyte and gametophyte generations are observed. The primary plant body is the diploid sporophyte.

Classification of Pteridophytes

The pteridophytes are classified into four classes as follows:

• Psilopsida

These are the most primitive pteridophytes. Rhizoids are present, but no leaves are present. These plants have homosporous sporophytes.

• Lycopsida

Club moss is the common name for these species. They have a well-differentiated plant body with adventitious roots, stems, rhizome, and leaves. Both homosporous and heterosporous sporophytes exist.

• Sphenopsida

Horsetails are the common name for them. Roots emerge from nodes of the underground rhizome, stem, and scaly leaves on these plants, which have a well-differentiated plant body. They are all the same.

• Pteropsida

The common name for them is ferns. The sporophyte is differentiated into stem, root, and curled leaves. The rhizomes are mostly short and strong. They're all alike.

The Life Cycle of Pteridophytes

The life cycle is a continuous reproductive process dominated by the sporophyte (sexual) stage of a generational alternation. Fern spores are launched into the air, developing into heart-shaped haploid gametophytes with both male and female sex organs. The sex organs of the young gametophyte become active as it matures. The antheridium is the male reproductive organ in ferns, and it contains and releases sperm. The archegonium is the female reproductive organ, with the egg at its base. Water is needed for fern reproduction since sperm must swim to the archegonium and fertilize the egg.

The sporophyte stage of the fern's life cycle is the most significant. The sporophyte is diploid, which means that all of its chromosomes are duplicated twice. The sporophyte produces haploid spores from its cells (one copy of chromosomes). The haploid gametophyte develops from these spores. Female structures (archegonia) and male structures (archegonia) are found in the gametophyte (antheridia). Fertilization is how the male sex cells (sperm) and female sex cells (eggs) join together. The genetic materials of both sperm and ovule combine to create a diploid zygote, which then develops into the sporophyte.

The presence of water is needed for sporophytes to remain genetically stable. Many gametophytes release a significant amount of sperms that swim in the same water as the archegonium. As a result, sperm cells from the same gametophyte do not always fertilize the egg of the same gametophyte. Inbreeding could increase harmful recessive alleles if this opportunity for cross-fertilization is lost.

A fertilized egg, or zygote, develops roots, stems, and a new sporophyte through mitosis (cell division). Embryonic sporophytes emerge as fiddleheads, tightly curled structures that unfurl as they mature into fronds (leaf-like structures). The sporophyte is the mature frond, which has several clusters of sporangia, which are sacs that bear asexual spores. Meiosis produces spores, which are then released into the air, continuing the life cycle.

Content and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for 

• Bachelors of Science in Biology   
• Bachelors of Science in Botany
• Master of Science in Botany

Related Concepts

1. The life cycle of pteridophytes
2. The life cycle of gymnosperms
3. The life cycle of angiosperms