Moss Life Cycle – Diagram and Reproduction   Recently updated !


Moss Life Cycle

The moss life cycle is a fascinating example of alternation of generation in plants. Mosses are small, non-vascular plants that typically form dense green clumps or mats, often in moist or shady locations. They belong to the division Bryophyta and are among the simplest and oldest groups of plants, having evolved around 450 million years ago. Despite their modest size and simple structure, mosses play vital ecological roles, including soil formation, water retention, and providing habitats for various microorganisms.

Key Points About the Moss Life Cycle

  • The life cycle alternates between haploid gametophyte and diploid sporophyte generations.
  • The gametophyte generation is dominant and photosynthetically active.
  • Fertilization requires water for the motile sperm to reach the egg.
  • The sporophyte depends on the gametophyte for nutrients.
  • Spores produced in the sporangium disperse and germinate into new gametophytes.

Background Information

What Are Mosses?

Mosses are non-vascular plants, meaning they lack the complex vascular tissues (xylem and phloem) found in higher plants that transport water, nutrients, and sugars. Instead, mosses move water and nutrients through their tissues using diffusion and capillary action. Structurally, a moss has a stem-like central axis (the gametophyte) and leaf-like structures that perform photosynthesis.

Key Characteristics of Mosses

Mosses have several characteristics that distinguish them from other types of plants:

  • Non-vascular: Lack xylem and phloem.
  • Simple Structure: Consist of a gametophyte with leaf-like structures.
  • Moisture Dependence: Require moist environments for reproduction and nutrient absorption.
  • Alternation of Generations: Life cycle alternates between a haploid gametophyte and a diploid sporophyte.

Mosses vs. Other Plants

Moss is a type of nonvascular plant. Ferns, flower, and trees are examples of vascular plants. Algae, while photosynthetic, is separate from plants.

  • Mosses vs. Vascular Plants:
    • Mosses do not have vascular tissues, while vascular plants do.
    • Mosses have a dominant gametophyte generation, whereas vascular plants (including ferns) have a dominant sporophyte generation.
    • Mosses rely on water for fertilization, while many vascular plants do not.
  • Mosses vs. Algae:
    • Mosses are terrestrial, whereas algae are primarily aquatic.
    • Mosses have differentiated tissues (e.g., stem-like and leaf-like structures), while many algae are undifferentiated.
    • Mosses have a more complex life cycle involving alternation of generations, whereas algae have simpler or equally complex life cycles depending on the species.

The Moss Life Cycle

The moss life cycle involves alternation of generations. What this means is that the plant alternates between a multicellular haploid (gametophyte) and a multicellular diploid (sporophyte) phase.

1. Gametophyte Generation

The dominant and more conspicuous stage in the moss life cycle is the gametophyte generation. When you see a layer of green moss, this is its gametophyte stage. This stage contains chlorophyll and performs photosynthesis. It is haploid (having one set of chromosomes) and develops from a spore. The gametophyte consists of a stem-like structure with leaf-like appendages and anchors itself to the substrate using rhizoids.

  • Formation of Gametangia: The gametophyte produces specialized structures called gametangia. The gametangia is where gametes are formed. There are two types of gametangia:
    • Antheridia: Male structures that produce motile sperm.
    • Archegonia: Female structures that produce eggs.

Some mosses are monoecious, while others are dioecious. In monoecious mosses, both male and female structures occur on the same plant. In dioecious mosses, these structures are on separate gametophyte plants.

2. Fertilization

Fertilization in mosses requires water because the motile sperm need to swim to the egg. When water is present, the sperm released from the antheridia swim to the archegonia, where fertilization occurs, resulting in the formation of a diploid zygote. Moss also make use of tiny arthropods, like mites and springtails, that carry moss sperm and aid in fertilization (much like how insects pollinate vascular plants).

3. Sporophyte Generation

The diploid zygote remains within the archegonium and grows into the sporophyte, which is nutritionally dependent on the gametophyte. The sporophyte consists of three main parts:

  • Foot: Anchors the sporophyte to the gametophyte.
  • Seta: A stalk that elevates the sporangium.
  • Sporangium (Capsule): The site of spore production through meiosis.

Inside the sporangium, diploid cells undergo meiosis and produce haploid spores. When mature, the capsule releases the spores into the environment.

4. Spore Dispersal and Germination

The haploid spores disperse through the wind or water. When they land in a suitable environment, they germinate into protonemata, which are thread-like structures that eventually develop into a new gametophyte, thus completing the life cycle.

Glossary of Terms

The key to understanding the moss life cycle is mainly learning the terminology for the parts of the plant:

  • Antheridia: Male gametangia that produce sperm.
  • Archegonia: Female gametangia that produce eggs.
  • Gametangia: Structures that produce gametes.
  • Gametophyte: The haploid stage that produces gametes.
  • Protonemata: Early stage in the moss life cycle that develops from spores and grows into the gametophyte.
  • Rhizoids: Root-like structures that anchor the gametophyte.
  • Seta: The stalk of the sporophyte that supports the sporangium.
  • Sporangium: The capsule of the sporophyte where spores are produced.
  • Sporophyte: The diploid stage that produces spores.

References

  • Budke, Jessica M; Bernard, Ernest C; Gray, Dennis J; Huttunen, Sanna; Piechulla, Birgit; Trigiano, Robert N (2018). “Introduction to the special issue on bryophytes”. Critical Reviews in Plant Sciences. 37 (2–3): 102–112. doi:10.1080/07352689.2018.1482396
  • Cronberg, N.; Natcheva, R.; Hedlund, K. (2006). “Microarthropods Mediate Sperm Transfer in Mosses”. Science. 313 (5791): 1255. doi:10.1126/science.1128707
  • Puttick, Mark N.; et al. (2018). “The Interrelationships of Land Plants and the Nature of the Ancestral Embryophyte”. Current Biology. 28 (5): 733–745.e2. doi:10.1016/j.cub.2018.01.063
  • van der Velde, M.; During, H. J.; van de Zande, L.; Bijlsma, R. (2001). “The reproductive biology of Polytrichum formosum: clonal structure and paternity revealed by microsatellites”. Molecular Ecology. 10 (10): 2423–2434. doi:10.1046/j.0962-1083.2001.01385.x