Bryophytes Notes

KINGDOM VIRIDIPLANTAE: SUBKINGDOM STREPTOBIONTA

• Embryophyte Clade: Plants exhibiting heteromorphic alternation of generations.
• Adapted to terrestrial existence.
• Produce gametangia with sterile tissue.
• Develop from an embryo.

Plant Phylogeny Overview

• Praesinophytes, Chlorophytes, and Glaucophyta: Represent earlier diverging lineages.
• Basal Streptobionts: An intermediate group in green plant evolution.
• Bryophytes: Non-vascular plants including mosses, hornworts, and liverworts.
• Vascular Cryptogams: Seedless vascular plants.
• Gymnosperms and Angiosperms: Seed-bearing vascular plants.

Bryophytes: Non-Vascular Embryophytes

• Bryophytes are a paraphyletic group, not a single division.
• Divided into:
  • Mosses (Bryophyta)
  • Hornworts (Anthocerotophyta)
  • Liverworts (Marchantiophyta)
• Lack vascular tissue.
• Generally small in size.
• Gametophyte is the dominant, photosynthetic stage.
• Sporophyte is usually parasitic on the gametophyte.

PHYLUM MARCHANTIOPHYTA: The Liverworts

• Gametophyte:
  • Photosynthetic.
  • Exhibits indeterminate growth, originating from a protonema.
• Gametophores:
  • Stalks arising from the gametophyte body.
  • Bear gametangia at their tips: antheridia (male) and archegonia (female) on the head disk.

Liverwort Sporophyte

• Short-lived and determinate in growth.
• Develops within the archegonium.
• Consists of a foot, seta, and capsule.
• Sporogenous tissue within the capsule undergoes meiosis to form tetrad spores.
• Most liverworts have dehiscent capsules.
• Two types of liverwort thallus (plant body):
  • Thallose/thalloid type
  • Leafy type

CLASS MARCHANTIOPSIDA ORDER MARCHANTIALES

• Gametophyte is thalloid with dichotomous branching.
• Prostrate growth habit (lying flat).
• Possess upright gametophores:
  • Antheridiophore (male)
  • Archegoniophore (female)
• Dehiscent capsule.
• Example: Marchantia

MARCHANTIA

• Grows on moist soil and dripping walls, protected from direct sunlight.
• Emits a citrus-like odor.
• Thalloid structure contains air chambers (stomata).
• Rhizoids anchor the plant.

Leafy liverwort

• Description of leafy liverworts

Male Gametophyte Structures in Marchantia

• Antheridial head disk
• Antheridia
• Antheridiophore
• Scale bar: 500 \mu m

Female Gametophyte Structures in Marchantia

• Archegonium parts:
  • Neck canal cells
  • Venter containing the egg
• Archegonial head/disk
• Archegoniophore with sporophyte

Marchantia Sporophyte Details

• Elaters: Hygroscopic structures facilitating spore dispersal.
• Foot: Anchors the sporophyte to the gametophyte.
• Seta: Stalk connecting the foot and capsule.
• Calyptra: Protective covering over the capsule.
• Spores: Products of meiosis within the capsule, mixed with elaters.

Gemmae and Asexual Reproduction in Marchantia

• Gemmae: Asexual spores located in specialized cup-like structures (gemmae cups).
• Dispersal: Gemmae are dislodged by wind or rain.
• Development: Upon dispersal, gemmae grow into small thalli.

Marchantia Life Cycle

• Alternation of generations between gametophyte and sporophyte.
• Asexual reproduction via gemmae.
• Sexual reproduction involving antheridia (male) and archegonia (female).
• Sperm fertilizes the egg, forming a zygote. Zygote develops into a sporophyte (foot, seta and capsule) which will undergo meiosis to produce spores that germinate into new gametophytes.

PHYLUM ANTHOCEROTOPHYTA: The Hornworts

• Thallose gametophyte with epidermis and air chambers (stomata).
• Some hornworts have a symbiotic relationship with Nostoc (cyanobacteria).
• Each cell contains one large chloroplast with pyrenoids.
• Lack gametophores; archegonia and antheridia are found on the upper surface of the thallus.
• Sporophyte grows from the top of the foot.

CLASS ANTHOCEROTOPSIDA ORDER ANTHOCEROTALES

• Example: Anthoceros (hornworts)
• Capsule (sporangium) appears horn-like:
  • Indeterminate growth.
  • Dehisces along longitudinal slits.
  • Contains photosynthetic tissue and stomata.
  • Spores are dispersed with the aid of elaters.

Hornwort Sporophyte Structure

• Columella: Central sterile tissue within the capsule.
• Jacket layer: Outer layer of the capsule.
• Elaters: Aid in spore dispersal.
• Spores: Products of meiosis.
• Stoma: Pores for gas exchange.
• Epidermis: Outer protective layer.
• Rhizoid: Anchors the gametophyte.
• Meristem: Region of cell division for growth.

Phaeoceros, Hornwort

• Life cycle showing Sperm, Egg, Antheridium, Archegonium, Columella, Spores, Elaters etc..

PHYLUM BRYOPHYTA: The Mosses

• Complex and long-lived gametophyte with a somewhat ephemeral sporophyte.
• Rhizoids are complex, multicellular, and branched.
• Spore germinates to form a filamentous protonema.
• Leafy gametophytes have symmetrical "leaves".
• Stomata are present in the sporophyte.

Moss Sporophyte

• Sporophytes have a foot, seta, and capsule.
• Most capsules contain:
  • Dehiscent covering - operculum
  • Hygroscopic peristomal apparatus - aids in spore dispersal

Moss Capsule Structures

• Calyptra: Covers the operculum.
• Seta: Elevates the capsule.
• Operculum: Covers the opening of the spore capsule, falls off to reveal the peristome.
• Peristome Tooth: Hygroscopic teeth that control spore release.

Moss Gametophyte and Sporophyte

• Diagrammatic representation of moss structures, showing the relationship between the sporophyte (seta, capsule, operculum, peristome) and the gametophyte (leaves, stem, rhizoids).

Moss Archegonial Head

• Paraphysis (sterile filaments)
• Neck canal
• Venter containing the egg

Moss Antheridial Head

• Display of antheridia.

Moss Antheridium

• Sterile jacket
• Spermatogenous tissue
• Stalk

Bryophyte Life Cycle (Moss Example)

• Alternation of generations between gametophyte and sporophyte.
• Spores germinate into a protonema.
• Protonema develops buds, forming gametophytes.
• Sexual reproduction occurs in antheridia (male) and archegonia (female).

CLASS BRYOPSIDA ORDER BRYALES

• Genus: Mnium
• Common name: Carpet moss
• Structures: seta, operculum

CLASS SPHAGNOPSIDA ORDER SPHAGNALES

• Sphagnum (peat moss)
• Sporophyte capsule: shiny black.
• Sporangium: Contains spores.

SPHAGNUM MOSS IMPORTANCE

• Major component of peat.
• Peat is an accumulation of partially decayed vegetation.
• Sphagnum moss does not readily decay due to phenolic compounds in cell walls.
• Low temperature, pH, and oxygen levels inhibit decay of organisms, including human remains (e.g., Tollund Man).

Peatland

• A wet terrestrial ecosystem dominated by living sphagnum.

Peat and Peat moss Uses

• Peat is harvested for fuel.
• Peat moss is used as a soil conditioner.
• Used for packing plant roots for shipment.

Peatland: Carbon Reservoir

• Contains 30\% of world soil carbon (carbon reservoir).
• Helps stabilize atmospheric CO_2 concentration.
• Overharvesting of sphagnum may contribute to global warming.
• As global temperature rises, water levels of peatland continue to drop, releasing CO_2 and further contributing to global warming.

Peatland fires are global threat

• Damage to environment.

Tollund Man

• Peatland mummy dating from 405-100 B.C.E.
• The acidic, oxygen-poor conditions produced by Sphagnum can preserve human remains for thousands of years.

COMPARISON OF NON-VASCULAR EMBRYOPHYTE PHYLA.