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Classification of Bryophytes

Classification of Bryophytes

Plant evolution progressed in the following order: algae>bryophytes>pteridophytes>gymnosperms>angiosperms. Bryophytes, the second generation, comprise the largest percentage of plant life on Earth. Exhibiting higher levels compared to algae, they possess vascular tissues. They are less developed than their successors and lack flowers, seeds and spores. 

Table of Content

  • Classification of Bryophytes 
  • Liverworts
  • Hornworts 
  • Mosses
  • Practice Problems 
  • Frequently Asked Questions 

Classification of Bryophytes 

There are three categorisations of these plant types: 

  1. Liverworts or Hepaticopsida or Hepaticophyta
  2. Hornworts or Anthocerotopsida or Anthocerotophyta 
  3. Mosses or Bryopsida or Bryophyta 

Liverworts 

About: The liverworts are named so due to the structural resemblance of lobular gametophytes with the liver. 

Morphology: These gametophyte plants are observed to be either foliose or thalloid. The forms possess leaves devoid of midrib and dorsiventral. Contrastingly, thalloid possessed dichotomous branched leaves that are lobed and dorsiventral. The thallus cells comprise chloroplasts lacking pyrenoids. 

Physiology: Their physiology seems to be less complex, and the structure of rhizoids on prostate-shaped gametophytes is unicellular, aseptate and branched. The liverworts also possess pored air chambers for gaseous exchange along with photosynthetic cells. The pores are never closed for consistent exchange. Chloroplasts lack pyrenoid. 

Reproduction: They undergo both sexual and asexual reproduction. The sporogenous tissue is formed from endothecium. The reproductive organs are antheridium and archegonium, which develop diploid sporophytes and subsequently undergo meiosis. The developed gametophytes are photosynthetic and free-living. Asexual reproduction is evident through the gemmae formation inside gemma cups. These asexual buds are multicellular and green that are released to form new gametophytes. 

Examples: Marchantia and Riccia. 

Hornworts

About: The origin of these types of plants is unknown. They are considered to be the earliest formed land plants. However, the fossils date back to the Cretaceous period. 

Morphology: The gametophytic body exhibits a thalloid shape lacking internal differentiation. It is flat and dorsiventral. 

Physiology: Smooth-walled rhizoids are seen to attach to the gametophytes. The single chloroplast in cells is present with a pyrenoid. Amphithecium contributes to sporogenous tissues. The capsules comprise pseudo elaters and columella originating from endothecium. They contain stomata assisting in photosynthesis. 

Reproduction: Asexual or vegetative reproduction occurs through thallus or tuber fragmentation methods. It is seen in unfavourable conditions. Sexual reproduction occurs via waterborne sperm that reaches from its site of origin, antheridium, to the target site, archegonium. The product is a fertilised egg, further developing into a sporophyte. It further splits vertically to release spores capable of conversion into a gametophyte. 

Examples: Megaceros and Anthoceros.

Mosses

About: It is the largest class of Bryophytes. Their habitat is in harsh regions of extreme cold temperatures, such as the Arctic and Antarctic areas. They are air pollution sensitive and hence are used as indicator species to identify the pollution level. Their diversity has made them to be further divided into five orders. 

Morphology: They comprise leaf, stem and root-like structures like previous classifications, thus lacking true vascular tissues. Rhizoids serve the function of water absorption and anchor the stem-like axis. They are multicellular and have oblique septa. The leaves are also morphologically different from true leaves except for the green colour and flat blade with thick midrib. The gametophytes are observed to be foliose gametophores and protonema. The foliage lacks midribs. They also contain columella and capsule dehiscence occurs through lid separation. 

Physiology: The cells are haploid, lacking stomata and vascular strands. They possess specialised cells for food and water transportation representing the xylem and phloem. 

Reproduction: Vegetative reproduction occurs by fragmentation or budding of secondary protonema. Sexual reproduction occurs through antheridia and archegonia at leafy shoots' apex. They produce sporophytes that are differentiated to higher order compared to liverworts. 

Examples: Sphagnum and Funaria. 

Practice Problems

Q1. Which is the Bryophyte in the given options? 

A. Porphyra
B. Ulothrix
C. Marchantia 
D. Ginkgo

Ans. C. Marchantia 

Porphyra and Ulothrix are algae, while Ginkgo is a gymnosperm. 

Q2. What is the male reproductive organ in bryophytes?

A. Antherozoids
B. Gemmae
C. Antheridium
D. Archegonium

Ans. C. Antheridium 

The multicellular male sexual reproductive organ in bryophytes is the antheridium. 

Q3. What do zygotes form before undergoing meiosis?

A. They divide immediately for meiosis 
B. They undergo mitosis 
C. They form sporophyte 
D. None of the above 

Ans. C. They form sporophyte 

The sporophytes germinate through meiosis to produce gametophytes. 

Frequently Asked Questions

Q1. What is the reason for the high fertility of areas witnessing dense moss growth?
Answer:
The mosses grow densely on soils that resemble a mat. It reduces the damage that may occur due to rain by capturing the soil. The lesser extent of soil erosion leads to higher fertility of the region. 

Q2. What colonises rocks first?
Answer: 
The lichens and mosses are the first organisms to colonise rocks. 

Q3. What is the economic benefit of mosses?
Answer: 
The species of Sphagnum, which is a moss, serves numerous economical benefits. Due to its higher water retention capacity, the peat source finds usage as fuel and packing material for biotic components.

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