Lecture Notes: Mosses - The Tiny Forest Plants

Introduction

• Forest Composition
  • Dominated by large plants competing for light.
  • Mosses form a unique group of tiny plants on the forest floor.
  • Over 10,000 species of mosses exist.

Characteristics of Mosses

• Gametophytes
  • Mosses are gametophytes, meaning they are haploid with one set of chromosomes.
  • Small, compact form helps maintain upright stems.
  • Rhizoids anchor mosses to the soil.
  • Moisture accumulation around stems, forming a water film.

Reproductive Structures

• Male Structures (Antheridia)

  • Hairlike structures called paraphyses hold water around stems.
  • Complex organs with multiple cells, supported by a stalk.
  • Contain sperm cells.

• Female Structures (Archegonia)

  • Located at the tip of female stems.
  • Consist of a slender neck and a chamber called the venter.
  • Stalk attaches the archegonium to the moss stem.
  • Contain egg cells.

Reproduction Process

• Sperm Release and Transfer

  • Ideal conditions provided by rain for sperm release.
  • Sperm released into water droplets from antheridia.
  • Raindrops can transport sperm to female stems.

• Fertilization

  • Sperm use flagella to swim towards egg cells.
  • Archegonium releases sperm attractant.
  • Fertilization occurs upon fusion of sperm and egg nuclei, forming a diploid zygote.

Post-Fertilization Developments

• Zygote Development

  • Zygote remains in venter initially, forms an embryo.
  • Embryo grows into female stem for nutrient absorption.
  • Another end grows upward, splitting the venter.

• Sporophyte Formation

  • Formation of a long stalk (seta) lifting the venter into air.
  • Sporophyte forms attached to female stem, leading to sporangium development.

Spore Formation and Dispersal

• Spore Creation

  • Capsule contains fertile tissue with spores (sporocytes).
  • Meiosis produces tetrad of haploid nuclei, forming spores.
  • Spore cells develop thick resistant walls.

• Spore Dispersal

  • Capsule drys, revealing peristome teeth surrounding the opening.
  • Spores dispersed by wind, aiding colonization of new areas.

Mosses' Success Factors

• Adaptations
  • Use of both gametes and spores for reproduction.
  • Capability to thrive in diverse habitats from polar regions to tropics.
  • Ancient lineage dating back over 400 million years.
  • Small size contributes to their adaptability and success.

Conclusion

• Mosses are resilient, adaptable plants that successfully colonize a variety of environments.
• Their reproductive strategies and evolutionary history have enabled them to thrive globally.