Plant Form, Function, and Diversity

Plant Form, Function, and Diversity

Introduction

• This course covers the evolution and diversity of plants managed by environmental challenges such as reproduction, dispersal, and photosynthesis.

Core Concepts

1. Evolutionary History: Influenced by challenges related to reproduction, dispersal, and land-based photosynthesis.
2. Bryophytes: Non-vascular, small plants relying on surface moisture.
3. Vascular Plants: Possess internal tissues for water and nutrient transport, enabling deep rooting and vertical growth.
4. Gymnosperms: Seed plants that produce seeds and pollen within cones.
5. Angiosperms: Diverse group of seed plants that produce flowers and fruits.

Characteristics of Plants

• Plants are photosynthetic, fixed organisms with a distinctive life cycle featuring alternation of generations. They also grow strategically to acquire nutrients.

Cell Wall Functionality

• Cell walls limit mobility but provide structural integrity through:
  1. Turgor Pressure Maintenance
  2. Thickening with cellulose or lignin
  3. Facilitating vascular tissues for transporting water and nutrients.

Turgor Pressure Changes

• Turgor pressure can change based on solute concentration, affecting photosynthesis rates and leaf orientation.

Major Transformations in Plant Evolution

• Originating from green algae, plants have evolved through various adaptations:
  • Bryophytes and their evolution to vascular plants, eventually leading to gymnosperms and angiosperms.

Groups of Vascular Plants

1. Bryophytes (Nonvascular)
2. Pteridophytes (Vascular non-seeded)
3. Gymnosperms (Seeded)
4. Angiosperms (Flowering)

Bryophyte Characteristics

• Bryophytes:
  • Small, lacking roots, with haploid dominance.
  • Reproduce by spores, not seeds.
  • Include mosses (upright stalks), hornworts (flattened thalli), and liverworts (leafy/thalloid).

Bryophytes in Their Environments

• Hydration varies based on their surrounding environments:
  • Wet Environments: Active metabolism due to sufficient water absorption.
  • Dry Environments: Photosynthesis ceases when water is lacking.
  • Can inhabit niches like rocks or tree surfaces (epiphytes).

Sphagnum Moss

• Specialized for hydrating soil and influencing ecosystem carbon cycles by forming peat bogs that heavily store organic carbon.

Fossil Record of Vascular Plants

• Vascular plants appeared in the fossil record about 425 million years ago; xylem and phloem allowed increased size and hydration efficiency.
• Early vascular plants had branches but no true leaves.

Lycophyte Fossils and Diversity

• Early forms showcase specialized structures for resource uptake, and their leaves evolved independently with unique single-vein characteristics.
• Giant lycophytes from the Carboniferous era contributed to coal formation due to their slow decomposition in drying swamps.

Evolution of Woody Plants

• Evidence shows that woody plants evolved multiple times, demonstrating adaptations favoring taller growth.

Ferns and Horsetails

• Ferns: Characterized by tightly coiled leaves (fiddleheads) and underground stems.
• Horsetails: Exhibit jointed growth with high silica content and distinctive whorled leaf arrangements.

Aquatic Ferns: Azolla

• Utilized in agriculture as a biofertilizer, supporting nitrogen-fixing bacteria for rice cultivation.

Seed Plants

• Evolved mechanisms for reproduction without water, utilizing pollen for male gametophytes and nutrient-rich seeds for better dispersal and growth potential.

Gymnosperms

1. Cycads: Ancient lineage; cone-producing.
2. Ginkgos: Only one surviving species, Ginkgo biloba, known for pollution resistance.
3. Conifers: Tallest trees with needles, dominant in boreal forests.
4. Gnetophytes: Have a diverse fossil record showing significant evolutionary history.

Angiosperm Diversity

• Angiosperms exploded in diversity, especially after 100 MYA, now exceeding 380,000 species. Flowering plants benefit from varied pollination strategies, enhancing reproduction.

Eudicots

• First appeared 125 MYA. Distinguishing with two cotyledons and high conductivity xylem aiding in water transport and forest dominance.

Monocots vs. Eudicots

• Distinctive physical characteristics include differing leaf patterns, vascular bundle arrangements, and flower structures.

Grassland Expansion

• Grasses have thrived in the changing climate over 20 million years, accounting for nearly 30% of terrestrial ecosystems.

Conservation of Crop Plant Genetics

• Centers of origin provide genetic diversity critical for agriculture and food security, supporting crops like wheat, rice, and various vegetables.