Bryophytes & Ferns: Chapter 29 – Part 2

Introduction

This study guide covers the biology of bryophytes and seedless vascular plants (ferns and their allies), focusing on their life cycles, evolutionary relationships, structural adaptations, and ecological significance. These groups represent key stages in the evolution of land plants.

Plant Phylogeny and Major Groups

Overview of Plant Evolution

• Green Algae (e.g., Ulvophytes, Stoneworts): Aquatic ancestors of land plants.

• Nonvascular Plants: Includes mosses, liverworts, and hornworts. Lack true vascular tissue.

• Seedless Vascular Plants: Includes ferns, club mosses, whisk ferns, and horsetails. Possess vascular tissue but do not produce seeds.

• Gymnosperms: Vascular plants with "naked" seeds (e.g., Pines, Cycads, Ginkgo).

• Angiosperms: Vascular plants with seeds enclosed in fruit (flowering plants).

Key Innovations: Vascular tissue, roots, stems, leaves, seeds, and flowers evolved at different points in plant evolution.

Alternation of Generations

Life Cycle in Land Plants

All land plants exhibit alternation of generations, a life cycle in which multicellular haploid and diploid stages alternate.

• Gametophyte (N): Haploid, produces gametes by mitosis.

• Sporophyte (2N): Diploid, produces haploid spores by meiosis.

• Fertilization: Fusion of gametes forms a diploid zygote, which develops into the sporophyte.

• Spore: Haploid cell that can develop into a gametophyte.

Comparison: In bryophytes, the gametophyte is dominant; in vascular plants, the sporophyte is dominant.

Bryophytes: Structure and Life Cycle

General Characteristics

• Nonvascular: Lack true roots, stems, and leaves; do not contain true vascular tissue.

• Small size: Limited by lack of vascular tissue.

• Habitat: Typically found in damp, shady environments; some tolerate extreme dryness.

Major Bryophyte Groups

• Mosses (Phylum Bryophyta): Most diverse group; some have rudimentary conducting tissues.

• Liverworts (Phylum Hepaticophyta): Some have liver-shaped leaves; many reproduce asexually via gemmae.

• Hornworts: Less diverse; sporophytes have stomata and can perform photosynthesis.

Life Cycle Details

• Gametophyte Dominance: The gametophyte is the prominent, photosynthetic stage.

• Sporophyte: Small, dependent on gametophyte for nutrition.

• Sexual Reproduction: Gametes produced in specialized structures called gametangia (antheridia for sperm, archegonia for eggs).

• Water Requirement: Sperm are flagellated and require water to swim to the egg.

Table: Bryophyte Diversity and Life Cycle

Ecological and Economic Importance

• Sphagnum moss: Forms peat bogs, stores carbon, used in horticulture, wound dressing, and as fuel.

• Other mosses: Used in whisky production, as food for reindeer, and in various cultural products.

Seedless Vascular Plants (Ferns and Allies)

General Characteristics

• Vascular Tissue: Contains xylem and phloem; allows for larger size and efficient water/nutrient transport.

• True Roots, Stems, and Leaves: Present in most groups.

• Sporophyte Dominance: Sporophyte is the prominent, long-lived stage; gametophyte is small and short-lived.

Major Groups

• Lycophytes (club mosses): Ancient lineage, some show heterospory.

• Pteridophytes (ferns): Most diverse group; have large leaves called fronds.

• Horsetails and Whisk Ferns: Unique structural features; less diverse.

Life Cycle Details

• Sporophyte Dominance: Sporophyte is independent and photosynthetic.

• Gametophyte: Small, may be bisexual or unisexual; produces gametes by mitosis.

• Water Requirement: Sperm are motile and require water for fertilization.

• Sporangia: Spores produced in clusters called sori (in ferns).

Table: Seedless Vascular Plant Diversity and Life Cycle

Homosporous vs. Heterosporous Life Cycles

• Homosporous: Produce one type of spore; gametophyte is bisexual.

• Heterosporous: Produce two types of spores: megaspore (female gametophyte) and microspore (male gametophyte).

Example: Selaginella is a heterosporous lycophyte.

Prevention of Self-Fertilization

• Asynchronous maturity of gametangia reduces self-fertilization.

• Release of antheridiogen by early-maturing gametophytes promotes development of male gametophytes, increasing genetic diversity.

Ecological Impact of Early Land Plants

Effects on Earth's Atmosphere and Climate

• Early land plants converted atmospheric CO2 into decay-resistant tissue, reducing CO2 concentration.

• Lower CO2 led to cooler, drier climates, allowing plants to proliferate in new habitats.

• Seedless vascular plants contributed to the formation of coal deposits.

Key Terms and Definitions

• Gametophyte: Haploid, gamete-producing stage of the plant life cycle.

• Sporophyte: Diploid, spore-producing stage of the plant life cycle.

• Gametangia: Structures where gametes are produced (antheridia for sperm, archegonia for eggs).

• Sporangia: Structures where spores are produced.

• Homosporous: Producing one type of spore.

• Heterosporous: Producing two types of spores (megaspore and microspore).

• Sori: Clusters of sporangia found on the underside of fern fronds.

• Gemmae: Small multicellular bodies used for asexual reproduction in liverworts and some mosses.

Important Equations

• Meiosis in Sporophyte:

• Fertilization:

Summary Table: Comparison of Bryophytes and Seedless Vascular Plants

Additional info: Some details on the evolutionary innovations and ecological impacts were inferred from standard biology knowledge to provide a complete, self-contained study guide.