Bryophytes

Bryophytes

  • Bryophytes are also called ‘Amphibians’ of the plant kingdom because these plants can live in soil but are dependent on water for sexual reproduction.
  •  Bryophytes include the various mosses and liverworts that are found commonly growing in moist shaded areas in the hills.
  •  Bryophytes usually occur in damp, humid, and shaded localities.
  •  Bryophytes play an important role in plant succession on bare rocks/soil.
  •  The plant body of bryophytes is thallus-like and prostrate or erect, and attached to the substratum by unicellular or multicellular rhizoids.
  •  Bryophytes lack true roots, stems, or leaves. They may possess root-like, leaf-like, or stem-like structures.
  • The main plant body of the bryophyte is haploid. It produces gametes and, hence is called a gametophyte.
  •  The sex organs in bryophytes are multicellular.
  •  The male sex organ is called the antheridium. They produce biflagellate antherozoids.
  •  The female sex organ called archegonium is flask-shaped and produces a single egg.
  •  The antherozoids are released into water where they come in contact with archegonium.
  •  An antherozoid fuses with the egg to produce the zygote.
  •  Zygotes do not undergo reduction division immediately.
  •  They produce a multicellular body called a sporophyte.
  • The sporophyte is not free-living but attached to the photosynthetic gametophyte and derives nourishment from it.
  •  Some cells of the sporophyte undergo reduction division (meiosis) to produce haploid spores. These spores germinate to produce gametophyte.
  • Bryophytes are a group of non-vascular plants that represent one of the earliest land plant lineages.
  • They include mosses, liverworts, and hornworts, with mosses being the most diverse and well-known group.

Characteristics:

  1. Non-Vascular: Bryophytes lack specialized vascular tissues (xylem and phloem) for water and nutrient transport. This limits their size and habitat choices.

  2. Small Size: Most bryophytes are small in size, typically a few centimeters tall. Their diminutive stature is due to the absence of vascular tissues.

  3. Rhizoids: Bryophytes have simple, hair-like structures called rhizoids that anchor them to the substrate. These are not true roots but aid in anchorage and absorption of water.

  4. Moisture Dependency: Bryophytes require a moist environment because they lack the cuticle and stomata found in vascular plants, making them prone to desiccation.

  5. Alternation of Generations: Bryophytes exhibit an alternation of generations' life cycles.

    • The dominant, photosynthetic phase is the gametophyte (haploid), which produces gametes.
    • The sporophyte (diploid) is smaller and dependent on the gametophyte. It produces spores through meiosis.

Life Cycle:

  • Bryophytes have a life cycle with alternating generations: a haploid gametophyte and a diploid sporophyte.
  • The dominant and photosynthetic phase is the gametophyte.
  • The sporophyte is typically short-lived and dependent on the gametophyte for nutrition.

Reproduction:

  1. Asexual Reproduction: Bryophytes reproduce asexually by fragmentation or the production of specialized structures called gemmae.

  2. Sexual Reproduction: Bryophytes also reproduce sexually. Male and female gametangia produce sperm and eggs, respectively. Water is often required for sperm to swim to the egg for fertilization.

 

MOSSES

 

  •  Moss is a small simple nonvascular plant that has both stems and leaves, but ‘no roots’.
  •  The Mosses are considered nonvascular and are grouped with Liverworts because-
  •  Their vascular tissue is very simple.
  •  Both of them have similar life cycle.
  • The predominant stage of the life cycle of a moss is the gametophyte which consists of two stages.
  •  The first stage is the protonema stage, which develops directly from a spore. Protonema is a creeping, green, branched and frequently filamentous stage.
  •  The second stage is the leafy stage, which develops from the secondary protonema as a lateral bud. They consist of upright, slender axes bearing spirally arranged leaves.
  •  They are attached to the soil through multicellular and branched rhizoids. This stage bears the sex organs.
  •  Vegetative reproduction in mosses is by fragmentation and budding in the secondary protonema.
  • In sexual reproduction, the sex organs antheridia and archegonia are produced at the apex of the leafy shoots. After fertilisation, the zygote develops into a sporophyte, consisting of a foot, seta and capsule.
  •  The sporophyte in mosses is more elaborate than that in liverworts. The capsule contains spores. Spores are formed after meiosis. The mosses have an elaborate mechanism of spore dispersal.
  •  Common examples of mosses are Funaria, Polytrichum and Sphagnum.
  •  Moss is used as food for animals e.g., snails and worms eat moss.
  •  They help to hold soil in place to keep it from washing away.
  • Some mosses live on rocks and break them down to mud.
  •  Peat moss is added to soil to increase the amount of water it holds.

 

LIVERWORTS

 

  •  The liverworts grow usually in moist, shady habitats such as banks of streams, marshy ground, damp soil, and bark of trees and deep in the woods. It forms a slippery layer of green cells on the ground.
  •  The Liverworts are small simple nonvascular plant that does not have roots, stems, or leaves.
  •  H2O and other materials are distributed throughout their bodies by Osmosis and Diffusion.
  •  The plant body of a liverwort is thalloid, e.g., Marchantia.
  • The thallus is dorsiventral and closely appressed to the substrate.
  •  The leafy members have tiny leaf-like appendages in two rows on the stem-like structures.
  •  Asexual reproduction in liverworts takes place by fragmentation of thalli, or by the formation of specialized structures called gemmae. Gemmae are green, multicellular, asexual buds, which develop in small receptacles, called gemma cups located on the thalli.
  •  The gemmae become detached from the parent body and germinate to form new individuals. During sexual reproduction, male and female sex organs are produced either on the same or on different thalli.
  • The sporophyte is differentiated into a foot, seta and capsule. After meiosis, spores are produced within the capsule. These spores germinate to form free-living gametophytes.

Ecological Importance:

  1. Soil Formation: Bryophytes contribute to soil formation by trapping and retaining moisture, organic matter, and minerals, thus aiding in the development of more complex ecosystems.

  2. Indicator Species: Bryophytes can serve as indicators of environmental quality. Some species are sensitive to pollutants and can indicate changes in air and water quality.

  3. Habitat for Microorganisms: The damp environment provided by bryophytes can be a habitat for microorganisms and invertebrates.

Economic Uses:

  1. Horticulture: Some mosses are used in the horticultural industry as potting material or as a substrate for orchids and other plants.

  2. Peat Moss: Sphagnum moss is widely used as a component in gardening and in the production of peat moss, which is used as a soil conditioner and for fuel.

Evolutionary Significance:

  1. Land Plant Evolution: Bryophytes represent a significant step in the evolution of plants from aquatic to terrestrial environments. They were among the first plants to colonize the land.

  2. Absence of Lignin: Bryophytes do not contain lignin, a complex polymer found in vascular plants. This makes them useful in studying the evolution of plant cell walls.

Conservation:

  • Many bryophyte species are threatened by habitat destruction, pollution, and climate change. Conservation efforts are essential to protect their biodiversity and ecological contributions.