Bryophyta - Structure, Classification and Characteristics

Bryophyta is the scientific name for a simple group of plants called Bryophytes. Bryophytes are the most basic plants that may be found on land. The liverworts, hornworts, and mosses are three groups of non-vascular land plants (embryophytes) that belong to the land plant group known as bryophytes, which is occasionally regarded as a taxonomic division. Mosses are the only members of the Bryophyta in the strict sense. Bryophytes are typically small and prefer damp locations, though they can endure in drier conditions as well.

What are Bryophytes?

Bryophyta is the division of green plants, which refers to embryophytes. They are land plants, particularly non-vascular ones. There are around 20,000 different plant species in the bryophytes. Bryophytes do not produce flowers or seeds, but instead, gametangia and sporangia, which are enclosed reproductive organs. They create gemmae or fragments to reproduce asexually or sexually, respectively, using spores. The term "bryophyte" is derived from the Greek words "bron," which means "tree moss or liverwort," and "phutón," which means "plant."

Bryophytes are also known as amphibians of the plant kingdom because they can live in soil but require water for sexual reproduction. They are devoid of vascular tissues. They reproduce through spores rather than flowers and seeds. The plant body is thallus-like and prostrate or erect, with unicellular or multicellular rhizoids attaching it to the substratum. A bryophyte's only distinguishing feature is the absence of true vascular tissue.

Examples of Bryophyta

There are about 20,000 plant species in the bryophyte kingdom. The three subgroups of bryophytes are mosses, hornworts, and liverworts. Typical examples include:

• Liverworts: Calobryum, Marchantia, Riccia, Pellia, and Porella.
• Mosses: Sphagnum, Funaria, and Polytrichum.
• Hornworts: Anthoceros, Notothylas, and Megaceros.

Habitat of Bryophyta

Bryophytes may survive in a wide range of environments, altitudes, temperatures, and moisture levels. In harsh and varied ecosystems like the arctic and desert regions, they can be seen growing in shady and moist conditions. Since it does not rely on roots to get nutrients from the soil, it can thrive in places where vascularized plants cannot.

Some bryophytes have an extraordinary ability to endure extended periods of freezing and dryness, and when moisture is restored, photosynthesis is resumed. Many bryophytes thrive on the soil, the living or decaying materials of other plants, and the persistent residues of their own growth. A few are aquatic in nature, while others grow on the exposed rock surface.

General Characteristics of Bryophyta

Following are the characteristics of Bryophyta:

• The plant body is thallus-like, meaning it can be prostrate or erect. They lack true vegetative structure and have a root-like, stem-like, and leaf-like structure.
• Rhizoids, which can be unicellular or multicellular, adhere to it.
• Plants do not have a vascular system (xylem, phloem). And plants grow in damp and shady environments.
• The haploid gametophyte is the dominant part of the plant body.
• The three parts of the thalloid gametophyte are rhizoids, axis, and leaves.
• The photosynthetic gametophyte has multicellular sex organs. The antheridium produces flagellated antherozoids.
• The zygote becomes a multicellular sporophyte. A semi-parasitic organism that feeds on the gametophyte is the sporophyte.
• Sporophyte cells meiosis to form haploid gametes that form a gametophyte. Protonema is the name given to the juvenile gametophyte.
• An archegonium is shaped like a flask and produces one egg. Antherozoids combine with eggs to form a zygote.

Structure of Bryophyta

Following forms the structure of Bryophyta:

• The plant is small and erect about 1 cm in height.
• Structure consists of rhizoid (the root like structures) and simple sessile leaves (leaf-like structures).
• The gametophyte is classified as protonema or foliose gametophore. Foliose plants have a stem as an axis and leaves without a midrib.
• Rhizoids have multicellular structures with oblique septa.
• Elaters are absent and the sex organs are carried apically on the stem.
• The sporophyte is classified into three types: foot, seta, and capsule. Endothecium gives rise to sporogenous tissues.
• The capsule dehisces due to the separation of the lid, and Columella is present.

Classification of Bryophyta  

Bryophyta is divided into three classes, according to the most recent classification:

1. Anthocerotopsida (Hornworts)
2. Hepaticopsida (Liverworts)
3. Bryopsida (Mosses)

Anthocerotopsida (Hornworts)

This class contains approximately 300 species. Hornworts are another name for them. It only has one order, Anthocerotales. Examples include Anthoceros, Megaceros, and Notothylas.

The primary characteristics are as follows:

• The gametophytic body is a simple, flat, dorsiventral thalloid with no internal differentiation.
• Dorsally embedded in the thallus are sex organs. Each cell has one chloroplast that contains a pyrenoid.
• The sporophyte is divided into three parts: the foot, the meristematic zone, and the capsule.
• Amphithecium gives rise to sporogenous tissues. Rhizoids have smooth-walled cells.
• The columella is found in the capsule, which is made up of endothecium. The capsule contains pseudocraters.

Hepaticopsida (Liverworts)

This group includes liverworts, which are a type of bryophyte. It has approximately 900 species. Liverworts are the most basic bryophytes. They prefer moist rocks and wet soil to live in. Because they live near water, their chances of drying out are greatly reduced.

A plant is called a gametophyte. It is generally dichotomously branched and can be thalloid (flat) or ribbon-like (ribbon-like). Marchantia, for example, is linked to the soil by rhizoids. Other species, such as Porella, grow erect and are deceptively leafy, meaning they have a fake stem and leaves.

Hepaticopsida is further classified into four orders:

• Marchantiales (e.g. Riccia, Marchantia)
• Sphaerocarpales (e.g. Sphaerocarpos)
• Calobryales (e.g. Calobryum)
• Jungermanniales (e.g. Pellia)

The following are the main characteristics of the class Hepaticopsida:

• A gametophyte plant can be thalloid or foliose.
• Dorsiventral, lobed, and dichotomously branched thalloid forms
• Sex organs are carried dorsally within gametophytic tissues.
• The sporophyte is made up of only the capsule (in Riccia) or the foot, seta, and capsule (in Marchantia).
• Rhizoids are septate, branched, and unicellular.
• Endothecium gives rise to sporogenous tissues, and the capsule lacks a columella.

Bryopsida (Mosses)

Bryopsida (Mosses): The largest class of Bryophyta, with approximately 1400 species. They are commonly referred to as mosses. Examples include Funaria, Polytrichum, and Sphagnum.

The primary characteristics are as follows:

• The gametophyte is classified as protonema or foliose gametophore. Foliose plants have a stem as an axis and leaves without a midrib.
• Rhizoids have multicellular structures with oblique septa.
• Elaters are absent and the sex organs are carried apically on the stem.
• The sporophyte is classified into three types: foot, seta, and capsule.
  Endothecium gives rise to sporogenous tissues.
• The capsule dehisces due to the separation of the lid, and Columella is present.

Reproduction in Bryophyta

Bryophytes can reproduce sexually and asexually:

Sexual Reproduction

Antheridium (male organ) and archegonium (female organ) may coexist on the same or different thalli. They both produce sperm and eggs. A zygote is formed after fertilisation. The zygote develops into a diploid sporophyte, and a couple of sporophyte cells undergo meiosis to produce haploid spores. These spores develop into haploid gametophytes, which are free-living and photosynthetic organisms.

Asexual Reproduction

It occurs as a result of the formation of gemmae or the fragmentation process. Gemmae are created within gemma cups. Gemmae are multicellular and green in color, as well as asexual. After detaching from the parent plant, the gemma cup grows into a new plant.