Living organisms are classified into five different categories based on their methods of nutrition, cellular structure, modes of reproduction, body composition, etc. R.H. Whittaker gave the Five Kingdom classification. The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia.
Plant Kingdom
The Plants or plant kingdom is essential for the existence of all the living creatures on earth. The entire mankind depends on the resources obtained from plants. There are innumerable species and types of plants that give us a variety of products for our daily use. Humans and all the other animals on earth are depended directly or indirectly on plants for their existence.
The Plant Kingdom includes a variety of plants that are classified on the basis of the following criteria, whether a plant body contains well-defined body parts. i.e. stem, root and leaf. Presence of vascular system for conduction of water to different body parts of a plant. Presence or absence of flowers and seeds, if the seeds are monocotyledons or dicotyledons, and if the seeds are naked or enclosed in a fruit. The plants have additional features like they are eukaryotic (with a definite nucleus), multicellular, autotrophic (produce their own food), contain chloroplast and chlorophyll pigment for photosynthesis, etc. plants are autotrophic and synthesize their own food due to the presence of chloroplast.
Oxygen is the most important element for the survival of an organism which is produced by plants. They absorb the sunlight and carbon dioxide from the surroundings and convert them into oxygen through the process of photosynthesis. This oxygen is essential for the survival of all animals and humans. Also, they provide us with essential food and medicines.
Characteristics of Plant Kingdom
- Plants are multicellular eukaryotic organisms, plant cell contains an outer cell wall made up of cellulose and a large vacuole that help maintain water balance.
- Plants are stationary in one position.
- They reproduce asexually by vegetative propagation, spore formation, budding, and fragmentation or sexually by pollination.
- A plant cell has plastids that contain photosynthetic pigments called chlorophyll.
Classification of Bryophytes in order of Evolution
The Plant Kingdom is divided into two types: cryptogamic are non-flowering species of plants and other is phanerogamic plants with flower-like structures or flowers. Eichler further classifies the plants into 5 divisions in order of their evolution.
Cryptogamia: It contains non-flowering plant species, the reproductive organs are unorganized and not arranged in flowers. These plants reproduce asexually through spore formation without any involvement of flowers or seeds from it. These plants are also known as non-seed-bearing plants. The name cryptogamae means “Hidden reproduction” which suggests reproduction without seeds. It involves three divisions namely
- Thallophyta
- Bryophyta
- Pteridophyta
Phanerogamia: It contains plant species with flower-like structures or flowers. The reproductive organs are visible and arranged in flowers. These are the most important divisions in the plant kingdom and plants reproduce through the seeds present in flowers, the plants consist of visible reproductive structures. It mainly has two divisions;
- Gymnosperm (Plants with flower-like structure).
- Angiosperm (Plants with Real flowers).
Bryophytes
Bryophytes have false roots, false stems, and leaf-like structures. The vascular system is absent in these plants. The plants are terrestrial and attached to a substratum but require plenty of water for sexual reproduction. Actual vascular tissue is absent in these plants due to the absence of lignin but they have specialized tissues used for the movement of water and other substance in plants. These plants are also referred to as ‘Amphibians’ of the plant kingdom
Characteristics of Bryophytes
- The plants do not have true roots they have stems and leaf-like structures, the main body of the plant is more like a thallus and haploid.
- The plant body is a gametophyte.
- Bryophytes are simple plants that grow in moist and shady places. They are usually found in rainforests, arid forests, and humid regions.
- Instead of roots, they have rhizoids that help them to stay attached to the surface, but they cannot absorb nutrients like normal roots.
- The plants reproduce asexually through fragmentation, gemma cups, and budding in protonema. Sexual reproduction is done through gamete formation.
- Mosses produce spores from leaves that travel through water and grow in new locations. Water is necessary for mosses to grow and spread. In the absence of water, it dries out completely and survives, when in contact with water they revive and grow again.
- The Bryophytes are terrestrial green plants with no vascular tissues. Types included in this division are: Mosses – class Bryopsida (Eg. Funaria, Sphagnum, etc), Liverworts – class Marchantiopsida (Eg. Marchantia, Riccia, etc).
Habitat
- They are often found on decomposing animal waste, shaded cavern mouths, surfaces of leaves, salt pans, bases of quartz pebbles, and copper-rich substrates.
- Bryophytes also grow in humid or subtropical climates.
- They grow and form deep, soft carpets on rock surfaces and forest floors, branches of trees and shrubs, trunks, and sheathing trunks. Usually, Bryophytes tend to be found near watercourses.
- Many of them grow on soil or on the remains of their own growth, on living or decomposing waste material of other plants.
- Bryophytes are usually resistant to periods of extreme dryness and freezing, once the moisture is retained, they again resume photosynthesis.
- The main requirements for growth are a stable substratum for fixing with it, a medium that retains moisture, appropriate sunlight, favorable temperature, and a humid atmosphere.
- Bryophytes are necessary for wetland habitats, especially peatlands.
- The mosses lead to the development of waterlogged habitats of highly acid peatland, where decomposition is comparatively slow.
- These mosses create an extensive bog that can control the hydrology of most of the surrounding landscape by behaving like a huge sponge that absorbs and hold a large amount of water and influence the water table.
- Mosses reside on bare rock surfaces and initialize soil formation, which in turn creates a substratum for seed plants that invade mossy sites, and through their shading, it creates a shaded habitat suitable for other bryophytes.
Distribution and Abundance
Bryophytes are spread all around the world, from polar and alpine regions to the tropics. At times, the presence of water is essential for the sperm to swim to the egg. Bryophytes are not found in extremely arid sites or in seawater, although some are always found in damp environments in arid regions and some are found on seashores above the intertidal zone. A few bryophytes are aquatic. They are found in abundance where the climate is humid. The highest level of diversity is in the tropical and subtropical regions. In Northern Hemisphere where the areas are cool, the moss Sphagnum dominates the vegetation of peatland in such areas.
The pattern of the geographic distribution of bryophytes is mostly similar to those of terrestrial vascular plants. Few of the species and genera and families of bryophytes are universal and show wide distribution globally. This distribution is due to their presence from an extremely ancient group of plants. Also, the easily dispersible small gemmae and spores make the wide distribution more effortless.
Life Cycle of Bryophytes
The plants reproduce sexually through gametes and hence they are called gametophytes. Bryophytes are spore-producing plants. The sex organs are multicellular and present on the thallus of the plant. Archegonium is the female sex organ, it is a flask-shaped multicellular structure present on the thallus of the plant consisting of a single egg cell (Female gamete) and it is non-motile. The part on which the female sex organ is present is known as the Female gametophyte. Antheridium is the male sex organ and its presence classifies the part as a Male gametophyte. When both the male and female sex organs are present on the same thallus then it is termed a Bisexual Thallus or Bisexual Gametophyte. The gametophyte is haploid, therefore the Archegonium and Antheridium are haploid too. Antheridium produces male gametes known as antherozoids which have two flagella (Biflagellate) and are motile. The antherozoids move through the water and when they come in contact with the archegonium, internal fertilization takes place and a fusion between antherozoids and egg occurs, which produces a diploid zygote. The zygote remains in the archegonium, then undergoes mitotic cell division and develops into a diploid embryonic sporophyte. The growing embryo is covered by a structure called calyptra. The sporophyte is dependent on the gametophyte for nutrition. The cells in sporophyte undergo meiosis and produce haploid spores. When the spores germinate, they go through mitosis and produce new gametophytes.
The life cycle of Bryophytes.
Evolution of Bryophytes
The first-ever evidence marking the emergence of bryophytes was found in rocks collected from Argentina that date to be 443 million to 484 million years old. This evidence which occurs as fossils of spore-like structures and liverwort cryptospores was found in rocks laid down between 471 million and 473 million years ago. The cryptospores are considered the first known terrestrial plants and the fossil cryptospores found in the rocks state that plants invaded the land about 485 million to 500 million years ago. Other Bryophyte fossils occur during the period with the earliest vascular plants which is about 358 million to 382 million years ago, they are also structurally similar. The specimens are well preserved and show substantial cellular structure.
For mosses, the earliest evidence that appears distinctive is 251 million to 298 million years ago, but the detailed relationship is not clear. Well-preserved evidence of mosses and liverworts appears about 66 million to 2.6 million years ago. Mosses are mostly represented in this evidence, and species of wetland habitats predominate the record.
Importance and Uses of Bryophytes
- Bryophytes have the ability to initiate soil formation on lands where soil quality is weak and plants cannot grow easily.
- They maintain soil moisture and replenish nutrients and minerals in the soil.
- Some bryophytes are certainly used for assessing the productivity and nutrient content of forest types.
- They can also help in restoring the nutrients in forest vegetation.
- Sphagnum or peat mosses are used in horticulture and required to produce biofuel, and used in the extraction of organic products, in the production of whisky, and also used as insulation. So they are economically important bryophytes.
- The harvesting, processing, and sale of peat mosses is itself a massive industry.
- It is used as packaging material for storing living material as it can retain and hold water.
- During the study of various species of bryophytes, different biological phenomena have been discovered that have extensive influence on the development and research processes in areas such as genetics.
FAQs on Bryophytes
Question 1: Are Bryophytes called Amphibians of Plant Kingdom?
Answer:
Amphibians are organisms that survive on land as well as water and require water for reproduction and propagation, similarly, Bryophytes are terrestrial plants but they require water for sexual reproduction, fertilization, and movement of gametes.
Question 2: Explain Sexual reproduction in Bryophytes.
Answer:
Sexual reproduction – Antheridium produces the male gamete (sperm) and archegonium produces the female gamete (egg). The male and female gamete unite and form a zygote after fertilization. The zygote develops into an embryonic sporophyte. Sporophyte cells undergo meiosis and form haploid spores. These spores develop into a haploid young leafy gametophyte.
Question 3: Explain Asexual reproduction in bryophytes.
Answer:
Asexual reproduction – Fragmentation occurs in bryophytes due to the thallus body of the plant. Gemma cups are structures formed on the body of plants. Gemma buds are present inside the gemma cups and after detaching from the parent plant it grows into a new plant. Protonema is a thread-like chain of cells produced from the spores, it is the early stage of the gametophyte. The spores germinate to form a filamentous structure called protonema. While the protonema is growing using cell division, due to the phytohormone cytokinin, buds are developed which gives rise to gametophores, stems, and leaf-like structures.
Question 4: Explain the economic importance of Bryophytes.
Answer:
Bryophytes are important as they are the primary producers of energy-rich compounds required for the food cycles of aquatic animals. Many species of bryophytes are used as food. Peat is obtained from sphagnum a moss, which is used as fuel. It is also used as packaging material for the shipment of living items because of its water-holding capacity. Mosses form a dense layer on the soil thus reducing the impact of rainwater on land and preventing soil erosion. Some species of mosses are also used to cure hepatic diseases, skin diseases, cardiovascular diseases, and wound healing.
Question 5: State a few general characteristics of Bryophytes.
Answer:
- Bryophytes are found in varying sizes from a length of 20cm and a breadth of 5cm to 1mm in width and less than 1mm in length.
- The branching of the thallus is forked or completely irregular. The margin of the thallus is mostly smooth, but it may be rough, flat or curved inward or downward.
- Phyllids are leaf-like structure that is arranged in rows of two or three or more around a shoot or may be irregularly arranged.
- The shoot may appear flattened, the phyllids are attached to the shoot by an extended base and are mainly one cell layer thick.
Question 6: How do Bryophytes get their nutrition?
Answer:
Bryophytes use the photosynthetic activity of chlorophyll pigments in chloroplast to produce their nutrient materials. They also absorb water and dissolved minerals present over the surface of gametophores. In mosses, water and nutrients are transferred from the gametophore to the developing sporangium along the seta. A protective cuticle covers the seta, reducing water loss.