Biology: Hornworts and Liverworts

Gametophyte and Sporophyte Structure

• Gametophyte can be a rosette or ribbon-like thallus.
• Hornworts develop internal cavities filled with mucilage and inhabited by photosynthetic cyanobacteria, mainly Nostoc, giving them a blue-green hue.
• Horn-like sporophyte emerges from an archegonium located deep within the gametophyte.

Liverworts

• Liverworts derive their name from the similarity of their thallus to liver lobes; "wort" means "herb."
• The thallus in liverworts comprises distinct zones: photosynthetic zone, air chamber, and storage zone.

Sporophyte Structures

• In Anthoceros, the horn-shaped structure is a sporophyte, not a gametophyte.
• The mature sporophyte contains a multicellular capsule, a central columella, and a tissue layer that produces spores.
• Spores possess pseudo-elaters, which are multicellular and function in spore dispersal through hydroscopic movements.

Bryopsida (True Mosses)

• Bryopsida is the largest class of mosses, encompassing 95% of all moss species.
• Gametophyte features a protonema and erect leafy shoots, with persistent spirally arranged leaves and rhizoids.
• Sporophytes consist of foot, seta, and capsule, with a unique peristome architecture that aids in spore release.

Reproductive Structures and Processes

• Elaters in bryophytes are formed alongside spores and assist in their release during dry conditions.
• Asexual reproduction methods include fragmentation, gemmae formation, and tubers.
• Sexual reproduction is oogamous, involving the production of antherozoids in antheridia and eggs in archegonia.

Life Cycle and Alternation of Generations

• The life cycle involves fertilization of eggs by antherozoids, forming a diploid zygote that grows into a sporophyte.
• The sporophyte releases haploid spores which germinate into the gametophyte, continuing the cycle.

Peat Formation and Uses

• Peat forms via the compression and carbonization of partially decomposed vegetative matter in bogs, primarily involving Sphagnum moss.
• Sphagnum secretes acids that inhibit decomposition, allowing for significant accumulation of dead plant material.
• Peat is utilized as fuel, in the production of various chemicals, to enhance soil texture in horticulture, as surgical dressings, and as packing material.

Summary of Bryophyte Classes

• Classes of bryophytes include:
  • Liverworts (Hepaticopsida)
  • Hornworts (Anthocerotopsida)
  • True mosses (Bryopsida), which are unique for their peristome teeth.

Key Terminology

• Elater: Structures that aid in spore dispersal through humidity changes.
• Protonema: Initial stages of moss growth post-spore germination, capable of forming new plants.
• Capsule: Structure of the sporophyte that releases spores.