Bryophytes Habitats and Distribution

Habitats of Bryophytes

• Bryophytes can be found in various habitats, including tropical, temperate, and arctic regions, with high moisture conditions.
• Some bryophytes are xerophytic, growing in desert conditions with typically dry conditions.
• Few bryophytes are truly aquatic, with underwater forms, such as Riccia fluitans.
• Bryophytes can be found at elevations ranging from sea level to over 18,000 feet above sea level on mountains.

Habit of Mosses and their Relatives

• The plant body of bryophytes is thallus-like and more differentiated than that of algae.
• The thallus size can measure up to 1-2 centimeters in height and may be prostrate or erect, attached to the substratum by unicellular or multicellular rhizoids.

Structure and Form of Bryophytes

• Bryophytes are a collective term for three distinct divisions of non-vascular plants: mosses (Division Bryophyta), liverworts (Division Hepatophyta), and hornworts (Division Anthocerotophyta).
• There are approximately 23,000 different species of bryophytes, lacking true xylem or phloem.
• Liverworts, mosses, and hornworts have distinct characteristics, such as:
  • Mosses: have water-conducting cells called hydroids and food-conducting cells called leptoids, anchored by filamentous multicellular rhizoids.
  • Liverworts: have flattened, lobed, somewhat leaf-like bodies (e.g., Marchantia sp.), and grow prostrate rather than upright.
  • Hornworts: have chloroplasts in each cell, pores and cavities filled with mucilage, and are often rosette-like in form.

Land Adaptations

• Bryophytes have adapted to land environments through:
  • Possessing root-like rhizoids to absorb water from the soil.
  • Having a water-proof waxy coating on the surface of the epidermis to prevent water loss.
  • Possessing stomata-like structures for gaseous exchange.
  • Possessing multicellular sex organs surrounded by sterile jackets to protect them from drying out.

Alternation of Generation

• Bryophytes require an external source of water (rain or dew) to reproduce.
• Alternation of generations is a characteristic feature of their life cycle, with the gametophyte being the conspicuous and dominant generation.
• In all bryophytes, the sporophytes are permanently attached to the gametophytes, varying in their dependence on them.

Gametophytic Generation

• The gametophytic generation is the more conspicuous phase in the life cycle, being long-lived and dominant.
• It is independent, green, fleshy, and autotrophic.
• Gametophytic plant bodies consist of parenchymatous cells only, lacking thick-walled and lignified cells.

Sporophytic Generation

• The sporophytic generation is the less conspicuous phase, being short-lived and completely nutritionally dependent on the gametophyte.
• The sporophyte develops from the embryo and is the first stage in the diploid sporophytic generation.
• The sporophyte is differentiated into foot, seta, and capsule.

Life Cycle

• Reproduction is generally by vegetative and sexual means.
• Vegetative reproduction includes:
  • Fragmentation of thallus.
  • Production of gemmae in gemmae cups (in liverworts).
• Sexual reproduction is oogamous, with multicellular sex organs and a dependent sporophyte generation.

Sexual Reproduction

• Sexual reproduction involves:
  • Antheridia (male sex organs): stalked and globose, with one cell thick sterile jacket, producing biflagellate antherozoids.
  • Archegonia (female sex organs): flask-shaped, with one cell thick sterile jacket, containing egg cells.
• Fertilization requires water, with antherozoids attracted by chemicals in the mucilage and fusing with egg cells to form a diploid zygote.