Chapter 9 The-Bryophytes-Pioneers-of-the-Terrestrial-World

Understanding Bryophyte Origins

The Transition to Land

Paraphyletic Nature

Bryophytes represent a transition between green algae (charophytes) to vascular plants.

Early vascular plants looked like bryophytes

Paraphyletic

a taxonomic grouping that includes a common ancestor and some, but not all, of its descendants. It represents an incomplete clade

Three bryophyte phyla

• Marchantiophyta (liverworts)

• Bryophyta (mosses)

• Anthocerotophyta (hornworts)

Liverwort (male, female, and leafy) identification

Shared Ancestry with Charophytes

-Well-developed grana stacks

-Same photosynthetic pigment

-asymmetrical flagellated sperm (motile sperm)

-Phragmoplast and cell wall formation during division

-Oogamous Reproduction (sexual reproduction)

phragmoplast

a plant-specific, barrel-shaped structure of microtubules, actin filaments, and endoplasmic reticulum that forms between daughter nuclei during late cytokinesis

Land Plant Adaptations

-Sterile Jacket Layer (prevent desiccation)

-Embryo Retention (Zygote remains protected in archegonium)

-Sporopollenin Coating (meiospores coated in desiccant resistant sporopollenin for wind travel)

-Apical Meristems (growth zones at shoot and roots)

Bryophyte Key Structural Differences from Vascular Plants

-lack true xylem and phloem

-lack lignin (restrict height)

-Gametophyte Dominance (haploid n)

-Dependent Sporophyte (sporophyte attached to Gametophyte)

-Single Sporangium (Sporophytes are unbranched structures producing only one sporangium per fertilization event, limiting reproductive output.)

The Bryophyte Gametophyte: Form and Function (Thalloid Forms)

Thalloid bryophytes are non-vascular plants with a flat, ribbon-like, or heart-shaped body (thallus) that lacks true stems or leaves, characteristic primarily of liverworts and hornworts

The Bryophyte Gametophyte: Form and Function (Leafy Forms)

-primarily comprising most liverworts and all mosses

- non-vascular, spore-producing plants that thrive in moist, shaded habitats.

- small, thin (often one-cell thick) leafy structures arranged in two or three rows, allowing them to absorb nutrients directly from the air and surface

The Bryophyte Gametophyte: Form and Function (Rhizoid Anchoring)

Moss rhizoids are multicellular filaments,

while liverwort and hornwort rhizoids

consist of single elongated cells

Symbiotic Partnerships: Bryophytes frequently harbor…..

nitrogen-fixing cyanobacteria or form associations with

mycorrhizal fungi to enhance nutrient uptake in nutrient-poor environments.

Internal Physiology and Gas Exchange

-Surface Pores

-Cuticle Development

-Plasmodesmatal Connections

-Ancestral Plastids

Surface Pores

Thalloid liverworts like

Marchantia possess pores functionally analogous to

stomata, facilitating

CO_2 entry for photosynthesis

Cuticle Development

Waxy cuticle layers cover many bryophyte surfaces, significantly retarding water

loss while maintaining gas exchange capacity.

Plasmodesmatal Connections

Contain desmotubules—central tubular structures derived from endoplasmic

reticulum—enabling intercellular communication and transport

Ancestral Plastids

Some hornwort cells retain a single large chloroplast with pyrenoids, directly

reflecting their ancestral green algal origins.

Bryophytes Sexual Reproduction Dynamics

Water Requirement

Antheridia Structure

Archegonia Architecture

Fertilization Pathway

Water Requirement

Flagellated sperm cells require a continuous film of liquid water to swim toward

stationary eggs—the primary limitation on bryophyte reproduction

Antheridia Structure

Stalked, spherical male organs containing spermatogenous tissue surrounded by

a protective sterile jacket layer

Archegonia Architecture

Flask-shaped female structures featuring a long neck and swollen base (venter)

housing the egg cell.

Fertilization Pathway

Neck canal cells disintegrate at maturity, creating a mucilaginous fluid-filled

channel guiding sperm to the egg.

Phylum Marchantiophyta

The Liverworts

Riccia

one of the simplest

liverworts