Bryophytes: General Features, Classification, Economic Importance

Bryophytes are non-vascular terrestrial plants. They are small plants found in shady and damp areas. They do not produce flowers and seeds, so they belong to the cryptogam group. A bryophyte is an amphibian of the plant kingdom as they require water as part of their life cycle. The term bryophyte was given by Brown. The study of bryophytes is called Bryology. The father of Bryology is Hedgwig, and the father of Indian Bryology is Shiv Ram Kashyap. The Bryophyta group includes embryophytes, such as mosses, liverworts, and hornworts.

General Features of Bryophytes

1. Habitat: They are found in damp, humid, and shaded regions. Some can be found in aquatic conditions too. Example: Riccia flutians, Ricciocarpous, Fontinalis.
2. Nutrition: They are mainly autotrophic. Certain species can be saprophytes, such as Buxbamia, Cryptothallmus, and epiphytes (Plants attached to another plant for attachment only, so they are also referred to as space parasites) such as Frullania.
3. Plant Body: The dominant phase or the main plant body is the-living haploid gametophyte, and the diploid sporophyte is dependent on the gametophyte.
4. The gametophyte is the haploid stage of the plant, which produces haploid gametes by the process of mitosis; hence it is called gametophyte.
5. Sporophytes are diploid stages of plants that produce haploid meiospores by meiosis. They receive nourishment from the gametophytes and produce haploid meiospores.
6. Instead of the true stem, true root, and true leaf, they have cauloid, rhizoid, and phylloid.
7. They are non- tracheophytes, i.e., they do not have vascular tissue (xylem and phloem).
8. Reproduction: Bryophytes can reproduce three ways:
   a. Vegetative Reproduction: It can be performed by fragmentation, tubers, buds, adventitious branches, gemmae.
   b. Asexual Reproduction: It mainly occurs by fragmentation and gemma cup. Mitospores (spores formed by mitosis) are absent from bryophytes onwards.
   c. Sexual Reproduction: They are oogamous in nature.
   The gametophyte of bryophyte has multicellular and jacketed sex organs. Antheridium is the male sex organ, and archegonium is called the female sex organ.

9. Antheridium is club-shaped and stalked surrounded by the sterile jacket which covers the sperm mother cell/androcytes/androgonial cells, which undergoes mitosis to form biflagellate antherozoids (male gamete), which is released in water.
10. Archegonium is flask-shaped and stalked with a tubular neck and swollen venter surrounded by the sterile jacket. The neck encloses a few sterile neck canal cells (NCC), and the venter contains one sterile venter canal cell (VCC) and fertile egg cell/ oosphere. The four lid cells cover the top of the neck region.

11. At maturity, the VCC and NCC degrade to form mucilage and absorb water, causing swelling of the archegonium. Pressure builds up on the lid cell, causing it to burst. The mucilage and certain chemicals (sucrose, K^+, and certain proteins) are released into the water, causing a chemotactic movement of antherozoids towards the oosphere.

12. Fertilization produces a diploid zygote which is formed inside the archegonia. The zygote undergoes mitotic division to form the diploid embryo, which further develops into a diploid sporophyte.
13. A sporophyte forms on top of a gametophyte and derives nutrition from it.
14. There are three parts in the sporophyte of bryophytes, namely foot, seta, and capsule. Inside the capsule, the spore mother cell undergoes meiosis to produce haploid meiospores.
15. Bryophytes are homosporous (Produce only one type of spore), which gets disseminated by the wind.
16. When the spores fall on suitable substratum, they germinate directly into the thalloid gametophyte (in Liverworts) or through a filamentous stage called protonema (in Mosses).

Classification of Bryophytes

Bryophytes can be classified into three classes:
A. Hepaticopsida (Liverworts)
B. Anthocerotopsida (Hornworts)
C. Bryopsida (Mosses)

Let us study each class of bryophytes:

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A. Hepaticopsida (Liverworts)

i. The plant body of liverworts is thalloid (in Marchantia) and leafy (in Porella) with tiny leaf-like appendages.
ii. The thallus is dorsiventral with unicellular rhizoids containing many chloroplasts without pyrenoids.
iii. Asexual reproduction is accomplished through fragmentation or by the development of a specialized structure called a gemme. Located on the thallus are the gemmae, which are eight-shaped, stalked, multicellular asexual buds. The gemmae cup is a cup-like structure that produces the buds. Mature gemmae detach from the parent body and germinate to form a new individual.

iv. During sexual reproduction, the sex organ, antheridia (male) and archegonia (female), are produced either on the same (Riccia) or on different thalli (Marchantia). The sex organs of Marchantia are located on stalked receptacles. The male sex organs are present on the antheridiophore, and female sex organs are formed on the archegoniophore.

v. When male and female gamete fuse, it forms a zygote that develops into an embryo that further develops to form a diploid sporophyte.
vi. Foot, seta, and capsule are the three parts of the sporophyte. In Riccia, there is only the capsule, no foot or seta.
vii. Spores on liberation produce haploid-living gametophytes.
viii. When male and female gamete fuses, it results in the formation of a zygote.

B. Anthocerotopsida (Hornworts)

i. The gametophytic body is flat, dorsiventral with unicellular, unbranched rhizoids.

ii. Sex organs are dorsoventrally embedded in the thallus.

iii. The sporophyte is differentiated into foot, meristematic zone, and capsule. Their sporophyte is erect horn-like, so that’s why they are called hornworts.

iv. Hornworts sporophyte is photosynthetic, so it depends on gametophyte only for mineral, water, and attachment, i.e., they are called partial parasites.

v. Each cell has only one chloroplast with a kidney-shaped chloroplast.

vi. Common examples of hornworts are Anthoceros, Notothylas, Megaceros.

C. Bryopsida (Mosses)

i. The gametophyte of mosses is differentiated into protonema and leafy stages.

ii. The plant body is a leafy gametophyte that has multicellular and branched rhizoids. They consist of upright, slender axis-bearing spirally arranged leaves.

 iii. In sexual reproduction, the sex organs antheridia and archegonia are produced on the same plant (monoecious)  at the top of the leafy shoot (acrocarpous) but with different branches (autoicous).

iv. Each antheridium produces several biflagellate antherozoids, and archegonium produces a fertile egg.

v. With the help of water, gametes fuse to form a diploid zygote, which develops into a sporophyte with the foot, seta, and capsule. 

vi. Capsule encloses a sporophytic mother cell, which undergoes meiosis to form haploid meiospores. In the mosses, the spores are dispersed by an elaborate mechanism known as peristomic teeth present in the operculum of the capsule.

vii. The spores germinate to form a creeping, green, filamentous gametophyte called protonema.

viii. Protonema form buds that germinate to form leafy gametophytes.

ix. Common examples of mosses are Funaria, Polytrichum, and Sphagnum.

Life Cycle of Bryophyte

The bryophyte life cycle shows an alternation of generation between the haploid gametophyte and the diploid sporophyte. The life cycle is haplodiplontic.

1. The haploid gametophyte stage is independent and bears sex organs on the tip of the branches. The male sex organ is antheridium which is round or club-shaped, and the female sex organ is archegonium which is flask-shaped.
2. Anthredium has several androgonial cells or androcytes which divide mitotically to form male gametes called sperm or antherozoids.
3. Archegonium is flask-shaped and stalked with a narrow region called neck filled with neck canal cells (NCC), the neck region at the top is covered by lid cell, and the swollen region called venter with venter canal cell (VCC) and egg cell.
4. At maturity, NCC and VCC degrade to form mucilage and absorb water, creating pressure on the lid cell, causing the opening of the archegonium.
5. The mucilage contains chemicals when released in water, causing chemotactic movement of antherozoids towards the egg cell in archegonium.
6. Fusion of male and female gamete leads to the formation of the diploid zygote, which further develops to form a sporophyte.
7. The capsule of sporophyte contains sporophytic mother cell (SMC), which undergoes meiosis to form numerous haploid meiospores,
8. The haploid spores germinate to form a juvenile protonemal stage represented by a filamentous structure, which has buds on nodes giving rise to an erect leafy gametophyte.
9. This change from haploid stage to diploid stage is called alternation of generation.
10. Bryophyte shows a haplo-diplontic life cycle with sporic meiosis.

Economic Importance of Bryophytes

I. Prevention of Soil Erosion: A dense mat of bryophytes, specifically mosses, covers the soil, preventing soil erosion from rain.

II. Soil Formation: In rocky areas, mosses are an important connection in plant succession.

III. Lichens take part in forming soil in crevices of the rock. As a result of Sphagnum (bog moss) growth, ponds and lakes eventually fill with soil.

IV. Water Retention: Dry Sphagnum has great water-absorbing capacity. Gardeners employ this characteristic to keep seedlings and cut plants moist during transportation and propagation. It also helps to maintain high soil acidity.

V. Medicinal Use: Sphagnum moss is used as absorbent cotton in old age, also called cotton moss.

VI. Peat: Sphagnum is also called peat moss. They grow in acidic marshes. Peat is a dark, spongy mass formed by the gradual carbonization, compression, and fossilization of moss and other marshy plants over thousands of years. Peat is dried, compressed, and cut to form blocks. The peat blocks serve as fuel and good manure. It reduces soil alkalinity, increases water retention, and improves aeration.

Summary

Bryophytes are amphibians of the plant kingdom because they require water to complete their life cycle. They are generally found in damp and shady places. The dominant phase of the plant body is the gametophyte, which produces the haploid gametes. After fertilization, gametes fuse to form a diploid zygote in the archegonium, further dividing to form a sporophyte with foot, seta, and capsule. Capsule bears sporophytic mother cells, which undergo meiosis to form haploid meiospores, germinating to form the gametophytic body. Bryophytes are further classified into three classes Hepaticopsida (Liverworts), Anthocerotopsida (Hornworts), Bryopsida (Mosses).

Frequently Asked Questions (FAQs) on Bryophytes

Q.1. What are two examples of bryophytes?
Ans: The two examples of bryophytes are Riccia and Marchantia.

Q.2. What are the three classes of bryophytes?
Ans: The three classes of bryophytes are hornworts, liverworts, and mosses.

Q.3. What are the three components of sporophyte?
Ans: The sporophyte bears foot, seta, and capsule.

Q.4. Which plants are bryophytes?
Ans: The bryophytes are non-vascular, seedless plants that require water to complete their life cycle, so they are known as amphibians of the plant kingdom.

Q.5. Which is the aquatic bryophyte?
Ans: The aquatic bryophyte is Riccia fluitans.

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