Bryophyta – Structure, Classification and Characteristics

An organism is a living, organic system that functions as a separate entity. When an organism performs the various life processes in one form or another, it is considered to be alive. The occurrence of life processes can distinguish living organisms from non-living objects. Nutrition, movement, growth, reproduction, and respiration, as well as sensitivity and excretion, are all life processes performed by living organisms. All organisms are made up of cells. Taxonomy divides organisms into groups such as multicellular animals, plants, and fungi, or unicellular microorganisms such as protists, bacteria, and so on.

Bryophyta

• Bryophytes are also known as amphibians of the plant kingdom because they can live in soil but require water for sexual reproduction.
• Bryophyta, the division of green plants, refers to embryophytes, which are land plants, particularly non-vascular ones.
• These are small plants that grow in shady and damp conditions. 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. Some have specialized tissues that transport water, but they are not considered true vascular tissues due to a lack of lignin.
• Bryophytes are thought to have evolved from charophytes and are thought to be the first true plants to have evolved.
• The bryophyte’s main plant body is haploid, produces gametes, and is thus referred to as a gametophyte.
• The male sex organ is called antheridium, and it produces biflagellate antherozoids, while the female sex organ is flask-shaped and produces a single egg.
• For example, Around 20,000 plant species are classified as bryophytes. Bryophytes are classified as liverworts, mosses, or hornworts. Some common examples include:
  • Marchantia, Riccia, Pellia, Porella, Sphaerocarpos, and Calobryum are examples of liverworts.
  • Mosses include Funaria, Polytrichum, and Sphagnum.
  • Anthoceros, Notothylas, and Megaceros are hornworts.

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)

Reproduction

Sexual Reproduction

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.

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.

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.

Frequently Asked Question 

Question 1: Explain reproduction in Bryopsida. 

Answer:

• Asexual reproduction– Budding and fragmentation of the secondary protonema occur during asexual reproduction.
• Sexual Reproduction- Antheridia and archegonia are found at the apex of leafy shoots. Sporophytes, which are more differentiated than liverworts, are produced after fertilization. 

Question 2: What sets bryophytes apart from other plants?

Answer: 

Bryophytes are distinguished from other terrestrial plants (known as “tracheophytes”) by the absence of xylem, the internal water transport tissue found in vascular plants. In contrast, bryophytes get their water and nutrients from their leaves.

Question 3: Explain liverworts. 

Answer:

• Liverworts typically grow in moist, shady environments. A liverwort’s plant body is a thalloid, and the thallus is dorsiventral and tightly appressed to the substrate.
• Asexual reproduction in liverworts occurs through thalli fragmentation or the formation of specialized structures known as gemmae, which are green, multicellular, asexual buds that develop in small receptacles called gemma cups located on the thalli.

Question 4: Mention some ecological importance of Bryophytes. 

Answer: 

• They protect the soil by reducing the impact of falling rain. Because of their water-holding capacity, they reduce the amount of run-off water.
• They decompose the rock, allowing higher plants to grow on it. The acid secreted by lichens, as well as the death and decay of mosses, aid in soil formation.
• Because bryophytes grow densely, they act as soil binders.
• Mosses are important in bog succession. Mosses have the ability to transform the landscape from open soil to climax forest.

Question 5: What is the importance of Bryophyta in medical uses? 

Answer:

• Peat-tar is an antiseptic and a preservative. Sphagnol, a peat-tar distillate, is used to treat skin diseases.
• A dried sphagnum decoction is used to treat acute hemorrhage and eye infections. Polytrichum species have been shown to dissolve kidney and gall bladder stones.

Question 6: Mention some characteristics of Bryophytes. 

Answer:

• Plants in this category lack roots and instead have crude stems and leaves.
• Mosses expel spores from their leaves, which travel by water and create new mosses in new places.
• These roots, known as rhizoids, do not absorb nutrients in the same way that other plant roots do.
• They have “rhizoids” instead of roots, which aid in the plant’s ability to anchor to the surface.

Question 7: What is the importance of Bryophytes in seedbeds? 

Answer:

Because of its ability to retain water, it is used to root cuttings in seedbeds, greenhouses, and nurseries. Sphagnum is also used to keep soil acidity high, which certain plants require.