Bryophytes: Summary Notes

Bryophytes Overview

  • Bryophytes include liverworts, mosses, and hornworts; bryology is their study.
  • Found in diverse environments, mostly terrestrial; sensitive to atmospheric conditions, used as bioindicators.
  • Transitional between charophycean green algae and vascular plants.
    • Share chloroplasts with grana, asymmetrical motile cells, nuclear envelope breakdown during mitosis, phragmoplasts, oogamous sexual reproduction, zygote retention, and sugar transport to zygotes with charophycean algae.
    • Share male/female gametangia, zygote/embryo retention, multicellular diploid sporophyte with spores, multicellular sporangia, meiospores with sporopollenin, and apical meristem tissues with vascular plants.
  • Liverworts appeared first, followed by mosses. Hornworts are late divergent and related to vascular plants.
  • Evolutionary advancements include multicellular embryos, stomata (after moss divergence), persistent sporophytes, independent sporophytes, and xylem with tracheids (in vascular plants).

Bryophyte Structure and Reproduction

  • Sporic meiosis life cycle with heteromorphic alternation of generations.
  • Gametophytes are the most visible feature; can be thalloid (flattened) or leafy.
  • Gametophytes have pores (analogous to stomata), a cuticle, and rhizoids for anchorage and absorption.
  • Asexual reproduction via fragmentation or gemmae; sexual reproduction is oogamous.
  • Sperm produced in antheridia, eggs in archegonia; both have sterile jacket layers.

Fertilization and Development

  • Zygote retained in archegonium, nourished by female gametophyte (matrotrophy).
  • Placenta with transfer cells facilitates nutrient transfer.
  • Zygote develops into a sporophyte with foot, seta, and capsule/sporangium; remains attached to gametophyte.

Embryophytes and Spore Characteristics

  • Embryophytes include bryophytes, ferns, and seed plants; all have matrotrophic embryos.
  • Many spores compensate for lower fertilization rates in terrestrial habitats.
  • Spores with sporopollenin resist bacterial damage and desiccation.
  • Spores germinate into protonemata, the beginning of the gametophyte phase.

Bryophyte Phyla

  • Marchantiophyta: liverworts
  • Bryophyta: mosses
  • Anthocerotophyta: hornworts
  • Bryophytes (informal) vs. Bryophyta (taxonomic).

Liverworts (Marchantiophyta)

  • Named for liver-shaped appearance.
  • Clades: complex thalloid and leafy liverworts.

Complex Thalloid Liverworts

  • Example: Marchantia with dichotomous branching.
  • Internal tissues: upper epidermis with pores, chlorenchyma with air chambers, parenchyma, and lower epidermis with rhizoids/scales.
  • Gametangia on gametophores (antheridiophores/archegoniophores).
  • Unisexual gametophytes.
  • Sporophytes with foot, seta, capsule; spores mixed with elaters.
  • Asexual reproduction via fragmentation or gemmae in gemma cups.

Marchantia Life Cycle

  • Spores germinate into male or female gametophytes.
  • Male gametophytes have antheridiophores, female have archegoniophores.
  • Sperm swim to archegonia for fertilization, forming a diploid zygote.
  • Zygote develops into an embryo, nourished by the placenta.
  • Venter becomes calyptra.
  • Capsule produces elaters and spores via meiosis.

Leafy Liverworts

  • Appear to have stems/leaves; common in rainforests.
  • Leaves are one cell thick.
  • Antheridia on androecium, sporophyte surrounded by perianth.

Liverwort Orders

  • Marchantiales: Includes Marchantia.
  • Sphaerocarpales: Small, lacking pores/air chambers; dimorphic (small males, large females); dioecious; involucre present.
  • Monocleales: One genus (Monoclea); largest liverwort; thallose, homogeneous tissue; antheridia in receptacles, archegonia covered by involucre-like flap, elongated seta.
  • Metzgeriales: Simple thallose, lacking air chambers/pores/scales; sessile antheridia/archegonia; elongated seta; anacrogynous.
  • Jungermanniales: Have oil bodies; leaves either incubous or succubous.
  • Takakiales: Simple morphology, no rhizoids/pores; phillids present; closely related to mosses.

Mosses (Bryophyta)

  • Three classes: Sphagnidae (peat mosses), Andreaidae (granite mosses), Bryidae (true mosses).
  • Sphagnidae and Andreaidae appeared first.

Sphagnidae (Peat Mosses)

  • Common in wet areas.
  • Have pseudopodium and operculum.
  • Capsule discharges spores ballistically.
  • Protonema is a plate of cells; leaves have narrow cells and large, dead, colorless cells for water storage.
  • Forms peatlands; harvested for fuel/gardening.
  • Chemicals inhibit bacterial decomposition.

Andreaidae (Granite Mosses)

  • Small, dark mosses on acidic rocks.
  • Filamentous protonema with multiple cell rows.
  • Capsule has 4 longitudinal slits.

Bryidae (True Mosses)

  • Filamentous protonema with slanted cross walls.
  • Leafy gametophytes have hydroids (water conduction) and leptoids (food conduction).
  • Antheridial head forms a splash cup for sperm dispersal.
  • Sporophytes have a long seta and stomata.
  • Capsule covered by calyptra; operculum reveals peristome with hygroscopic teeth.

Moss Life Cycle

  • Spores form protonema with buds.
  • Unisexual gametophytes with antheridial/archegonial heads.
  • Sperm swim to archegonia.
  • Zygote grows into embryo inside archegonium.
  • Venter becomes calyptra.
  • Mature sporophyte with foot, seta, and capsule.
  • Capsule opens to expose peristome.
  • Spores formed by meiosis.

Moss Ecology

  • Cushiony/acrocarpic mosses: tight tufts, erect gametophytes in dry habitats.
  • Feathery/pleurocarpic mosses: creeping, branched gametophytes in humid habitats.

Moss Examples

  • Fissidens: Common in aquariums.
  • Physcomitrium: Urn moss, lacks peristome.
  • Splachnum: Petticoat/umbrella/dung moss, grows on dung/bones.
  • Mnium: Leafy gametophores with pendent capsules.
  • Fontinalis: Water moss, aquatic.

Hornworts (Anthocerotophyta)

  • Thalloid gametophyte with a single large plastid per cell.
  • Nostoc may be present.
  • Unisexual gametophytes.
  • Antheridia/archegonia formed in sunken cavities.
  • Sporophyte is an upright, elongated structure with foot and sporangium (no seta).
  • Has a meristem for continuous growth.
  • Capsule splits into two horns when mature.
  • Sporophyte is photosynthetic, has stomata, and a central strand of sterile cells.
  • Pseudoelaters present.

Bryophyte Summary (Table Comparison)

  • Marchantiophyta (Liverworts): 5200 species, thalloid and leafy, unicellular rhizoids, numerous chloroplasts.
  • Bryophyta (Mosses): 12,800 species, leafy, multicellular rhizoids, numerous chloroplasts.
  • Anthocerotophyta (Hornworts): 300 species, thalloid, unicellular rhizoids, single chloroplast.

Conclusion

  • Plants evolved from Charophycean green algae.
  • Bryophytes include liverworts, hornworts, and mosses.
  • Sporophytes differ among bryophyte groups.
  • Bryophytes are ecologically important.