Bryophytes

The term Bryophyta came from the word ‘Bryon’  which means moss and python means plants. Bryophyta includes embryophytes like mosses, hornworts, and liverworts. These are the plants that grow in shady and damp areas and are small in size. They lack vascular tissues. They reproduce through spores instead of producing flowers and seeds.  Despite the fact that most bryophytes lack complex tissue organization, they exhibit a wide range of forms and ecology. They are found all over the world and are relatively small in comparison to most seed-bearing plants. The study of bryophytes is called Bryology.

Why are Bryophytes Called Amphibians of Plants?

Bryophytes are called “amphibians of the plant kingdom” because they’re terrestrial plants but require water to finish their life cycle at the time of sexual reproduction.

General Characteristics of Bryophytes:

• Plants occur in damp and shaded areas.

• The plant body is thallus-like, i.e. prostrate or erect.

• It is attached to the substratum by rhizoids, which are unicellular or multicellular.

• They have a root-like, stem-like, and leaf-like structure and lack true vegetative structure.

• Plants lack the vascular system (xylem, phloem).

• The dominant part of the plant body is the gametophyte which is a haploid.

• The thalloid gametophyte is divided into rhizoids, axis, and leaves.

• The gametophyte bears multicellular sex organs and is photosynthetic.

• The antheridium produces antherozoids, which are flagellated.

• The shape of an archegonium is a sort of a flask and produces one egg.

• The antherozoids fuse with an egg to make a zygote.

• The zygote develops into a multicellular sporophyte.

• The sporophyte is semi-parasitic and dependent on the gametophyte for its nutrition.

• Cells of sporophyte undergo meiosis to form haploid gametes which form a gametophyte.

• The juvenile gametophyte is known as protonema.

• The sporophyte is differentiated into foot seta and capsule.

Classification of Bryophytes

According to the newest classification, Bryophyta is split into three classes:

1. Hepaticopsida (Liverworts)

2. Anthocerotopsida (Hornworts)

3. Bryopsida (Mosses)

A. Hepaticopsida (Liverworts):

The name hepaticopsida comes from the word “hepatic” which means liver. Liverworts come under this class. Liverworts are a type of bryophyte that belongs to this group. It has around 900 species. The most basic bryophytes are liverworts. They prefer moist rocks and wet soil to live in. Because they dwell near water, their chances of drying are much reduced. 

A gametophyte is a type of plant. It can be thalloid (flat) or ribbon-like (ribbon-like), and is generally dichotomously branched. Marchantia, for example, is linked to the soil by rhizoids. Other species, such as Porella, tend to grow erect and are deceptively leafy, that is, differentiated into a fake stem and leaves. The gametophyte provides nutrition and protection to the sporophyte. The sex organs form towards the terminals of the branches on the upper surface of the thallus. As in Marchantia, they sometimes form distinct branches on gametophytes called antheridiophores and archegoniophores.

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Hepaticopsida is Further Divided into 4 Orders:

1. Marchantiales (e.g. Riccia, Marchantia)

2. Sphaerocarpales (e.g. Sphaerocarpos)

3. Calobryales (e.g. Calobryum)

4. Jungermanniales (e.g. Pellia)

The Main Characteristics of the Class Hepaticopsida are:

• The gametophyte plant is either thalloid or foliose.

• Thalloid forms are dorsiventral, lobed, and dichotomously branched.

• Rhizoids are unicellular, branched, and septate.

• Sex organs are borne dorsally embedded in gametophytic tissues.

• The sporophyte is a compilation of only capsule (in Riccia) or foot, seta, and capsule (in Marchantia).

• The columella is absent in the capsule.

• Sporogenous tissues develop from endothecium.

Reproduction:

• Asexual Reproduction:

It takes place by the formation of gemmae or by the process of fragmentation. Gemmae are produced inside gemma cups. Gemmae are green and multicellular and are also are asexual in nature. The gemma cup develops into a newly born plant after detaching from the parent plant.

• Sexual Reproduction:

Sexual reproduction: Antheridium (male organ) and archegonium (female organ) could also be present on equivalent thalli or different thalli. They produce sperm and egg respectively. After fertilisation zygote is formed. The zygote develops into a diploid sporophyte, a couple of cells of the sporophyte undergo meiosis to make haploid spores. These spores become haploid gametophytes, which are free-living and photosynthetic.

B. Anthocerotopsida (Hornworts): 

There are around 300 species present during this class. They are commonly known as hornworts. It has only one order i.e. Anthocerotales. Examples: Anthoceros, Megaceros, Notothylas. This group of bryophytes is slightly more advanced than Bryopsida and Hepaticopsida in several ways. From a broad perspective, the gametophyte is very lobed and uneven. The sporophyte is not reliant on the gametophyte for sustenance or protection, except during the early stages of development. In the gametophytic tissue, antheridia and archegonia are somewhat submerged.

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The Main Features are:

• The gametophytic body is flat, dorsiventral, simple thalloid, and has no internal differentiation.

• Rhizoids are smooth-walled.

• Each cell has one chloroplast with a pyrenoid.

• Sex organs are present dorsally embedded in the thallus.

• Sporogenous tissues develop from amphithecium.

• Pseudoelaters are present in the capsule.

• The columella is present within the capsule, which originates from the endothecium.

Reproduction:

• Asexual Reproduction:

Vegetative propagation takes place by the process of fragmentation of thallus and by tubers, which are formed under unfavourable conditions.

• Sexual Reproduction:

They reproduce sexually with the help of waterborne sperm that travels from antheridium to archegonium. A fertilized egg develops into a sporophyte. The Sporophyte splits lengthwise to release spores which become a gametophyte.

C. Bryopsida (Mosses):

It’s an important class of Bryophyta with around 1400 species. They are commonly called mosses.  Most mosses, like liverworts, like wet environments. They grow equally well in relatively dry environments, unlike other bryophytes. Mosses, on the other hand, need water to reproduce, hence they usually grow into cushions or mats. Examples: Funaria, Polytrichum, Sphagnum.

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Bryopsida is Further Divided Into 5 Classes:

1. BryalesAndriales

2. Sphagnales

3. Polytrichales

4. Buxbaumiales

The Main Features are:

• The gametophyte is divided into protonema and foliose gametophore.

• Foliose is formed of the stem as an axis and leaves without a midrib.

• Rhizoids are multicellular with oblique septa.

• Sex organs are borne apically on the stem.

• Elaters are absent.

• The sporophyte is differentiated into foot, seta and capsule.

• Sporogenous tissues develop from endothecium.

• The columella is present.

• Separation of the lid is the result of the Dehiscence of the capsule.

Reproduction:

• Asexual Reproduction:

Asexual reproduction takes place by budding and fragmentation of the secondary protonema.

• Sexual Reproduction:

Antheridia and archegonia are present at the apical part of leafy shoots. After fertilization sporophyte is produced, which is more differentiated than liverworts. The gametophyte develops from the spores.

Examples of Bryophytes

Bryophytes consist of around 20,000 plant species. Bryophytes are divided into liverworts, mosses, and hornworts. Some common examples are:

Liverworts: Marchantia, Riccia, Pellia, Porella, Sphaerocarpos, Calobryum.

Mosses: Funaria, Polytrichum, Sphagnum.

Hornworts: Anthoceros, Notothylas, Megaceros.

Ecological Importance of Bryophytes

Bryophytes have great ecological importance. Mosses and lichens are the first organisms to colonize rocks.

• They decompose the rock making it suitable for the expansion of the higher plants. Soil formation takes place by the acidic secretion that causes the death and decay of mosses. 

• Bryophytes grow densely and act as soil binders.

• Mosses play an important role in bog succession. The thick mat formed of mosses forms a suitable substratum for the germination of hydrophilic seeds due to the presence of water and humus. In the meanwhile, the dead and decayed mosses and hydrophilic plants form a solid soil for mesophytic development.

• They prevent erosion of soil by reducing the impact of falling rain.

• They reduce the quantity of run-off water because of their water holding capacity. 

• They help in recycling the nutrients. 

• They act as a rock builder. These plants decompose bicarbonate ions resulting in the precipitation of insoluble calcium carbonate. The mineral deposit continues to increase and therefore extends over several hundred square feet.

Economic Importance of Bryophytes

Medicinal Uses:

• Sphagnum is employed in dressing as it has high absorptive power and a few antiseptic properties for filling absorptive bandages in replacement of cotton for the treatment of boils and discharging wounds

• Marchantia has been employed to cure pulmonary tuberculosis and affliction of liver

• The decoction of dried sphagnum is used in the treatment of acute haemorrhage and eye infections

• Peat-tar is antiseptic and used as a preservative. Polytrichum species has been shown to dissolve stone in the kidney and gallbladder

• Antibiotic substances are often extracted from certain bryophytes having antibiotic properties

In Research:

Mosses and liverworts are used in research in the field of genetics. The mechanism of sex determination within the plant is discovered in liverworts

Packing Material:

Dried mosses make superb packing for fragile goods like glassware, bulbs. For trans-shipment of living material like cuttings and seedlings as they need water retention capacity.

Food:

Some mosses provide food for herbaceous mammals, birds, and other mammals.

As Indicator Plants: 

Some bryophytes grow during a specialized area and may be used as an indicator for acidity and basicity of the soil. For E.g. Polytrichum indicated the acidity of the soil, Tortella species grow well within the soil rich in lime or other bases and occur as calcicoles.

In seedbeds:

Because of its water retention capacity, it is used in seedbeds, greenhouses, nurseries to root cuttings. Sphagnum is additionally wont to maintain the high soil acidity required by certain plants.

Peat Formation:

Sphagnum is additionally referred to as sphagnum. Peat is formed by slowing down the decaying process. The gradual compression and carbonization of partially decomposed vegetative matter in bogs produce a dark-coloured substance called Peat.

It is used as fuel, lower layers of peat from coal, peat is also used in the production of ethyl alcohol, ammonium sulfate, ammonia, dye, paraffin, tannins, etc. It improves soil texture in horticulture.

Formation of Stone:

The travertine rock deposits are extensively used as a building stone.

The life cycle of Bryophytes

The independent gametophyte generation, which generates the sex organs, sperm, and eggs, and the dependent sporophyte generation, which produces the spores, alternate generation in bryophytes. The bryophyte sporophyte, unlike vascular plants, usually lacks a sophisticated circulatory system and develops only one spore-producing organ (sporangium) rather than numerous. Furthermore, the bryophyte's gametophyte generation is usually perennial and photosynthetically independent of the sporophyte, which has a close relationship with the gametophytic tissue, particularly at the sporophyte's base or foot. The gametophyte, on the other hand, is dependent on the sporophyte in most vascular plants. The gametophyte is the long-lived and visible generation in bryophytes, while the sporophyte is the long-lived and visible generation in vascular plants. On the gametophore of bryophytes, structures resembling stems, roots, and leaves are seen, whereas these structures are found on the sporophytes of vascular plants. The sporophyte produces spores, which eventually grow into gametophytes. 

The haploid gametophyte and the diploid sporophyte have alternate generations in the bryophyte life cycle. During the gametophyte stage, the specialized sex organs, the antheridia (male) and archegonia (female) produce haploid gametes (male and female) (female). Flagellated sperm swim through the water or are carried by insects. When two haploid gametes (sperm and egg) combine to form a diploid zygote, a diploid zygote is created. Bryophyte zygote develops inside archegonia and becomes a diploid sporophyte, as mentioned above. Mature sporophytes stay connected to the gametophyte and produce haploid spores in the sporangium through meiosis. These spores disseminate and become new gametophytes in the presence of favourable environmental circumstances.

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