Seedless Plants

Seedless Plants Overview

Introduction to Seedless Plants

• Focus on Kingdom Plantae and their evolution from green algae.

• Early plants transitioned from water to land, facing challenges:

• Strategy development to avoid drying out (desiccation).

• Need for structural support.

• Capturing sunlight for photosynthesis.

• Effective dispersal of reproductive cells.

• Seed plants have adapted to arid habitats while seedless plants typically thrive in moist environments.

Plant Evolution

Key Concepts

• Evolution of plants involved adapting to land.

• Importance of structural modifications that accompany this transition.

Plant Phylogeny

• Streptophytes: Includes Charophytes (green algae) and Embryophytes (land plants).

• Distinction between vascular and nonvascular plants:

• Nonvascular: Bryophytes (liverworts, hornworts, mosses).

• Vascular: Seedless plants (lycophytes, pterophytes, ferns, etc.).

• Further classification of land plants includes seed plants (
  Spermatophytes).

Alternation of Generations

• Plants show two dominant stages:

• Haplontic: Dominant haploid stage (gametophyte).

• Diplontic: Dominant diploid stage (sporophyte).

• In primitive plants, the gametophyte is predominant.

• As plants evolved, sporophyte generation became more dominant, with gametophyte getting smaller.

• Key life cycle terms:

• Gametophyte: haploid generation producing gametes.

• Sporophyte: diploid generation producing spores.

Apical Meristems

• Location of growth in roots and shoots.

• Apical meristems produce new cells, enabling growth and elongation.

• Protects root tips through the root cap as they penetrate soil.

Adaptations of Land Plants

• Transition to land involved significant adaptations:

• Nonvascular Plants: Initially limited to few inches in height.

• Vascular Tissue: Evolved to transport water (xylem) and photosynthetic products (phloem), allowing for greater height and capability to grow away from moisture sources.

• Other adaptations:

• Waxy cuticle helps prevent desiccation but also limits CO2 intake.

• Stomata for gas exchange, protective flavonoids against UVB damage.

• Development of secondary metabolites (e.g., alkaloids for defense).

The Evolution of Vascular Plants

• Vascular plants developed true roots, which enhance anchoring and nutrient absorption.

• Mycorrhizal relationships improve nutrient uptake.

• Development of leaves (microphylls and megaphylls) increased photosynthesis efficiency.

Seedless Vascular Plants

• Dominant sporophyte phase, dependent on water for reproduction.

• Major types include:

• Lycophytes: Club mosses, spike mosses, quillworts.

• Monilophytes: Horsetails, whisk ferns, ferns.

• Club mosses have microphylls; horsetails have silica in their tissue.

• Ferns are the most recognized group, thriving in moist environments with large compound leaves (fronds).

• Fern life cycles feature alternation of generations with clear dominant sporophyte phases.

Ecological Importance of Seedless Vascular Plants

• Mosses: Key role in tundra ecosystems.

• Ferns: Aid soil development, prevent erosion, help nutrient cycling, and may harbor nitrogen-fixing cyanobacteria.

• Use of peat moss in fuel and horticulture exemplifies their human utility and ecological function.

Notable Ecological Relationships

• Mycorrhizal Symbiosis: Close relationship between land plants and fungi aids nutrient acquisition.

• Nitrogen Fixation: Essential for plant growth, facilitated only by bacteria, underlining interconnectedness of soil flora.