30

Overview of Plant Diversity

• Chapter 30

  • Focuses on plant diversity, covering various groups and their adaptations.

Plant Groups

• Cuticle: Waxy layer on plant surfaces.

• Nonvascular Land Plants: Includes mosses, liverworts, and hornworts.

• Seedless Vascular Plants: Includes club mosses, ferns, whisk ferns, and horsetails.

• Gymnosperms: Group of plants with seeds not enclosed in an ovary.

• Angiosperms: Flowering plants; the most diverse group.

Leaf Tissue Anatomy

• Dermal Tissue: Protective outer covering of the plant.

• Ground Tissue: Includes palisade and spongy parenchyma for photosynthesis and storage.

• Vascular Tissue: Composed of xylem (water and nutrient transport) and phloem (food transport).

• Stomata: Pores for gas exchange, surrounded by guard cells.

The Evolutionary Origins of Plants

• Definition: Plants are organisms that evolved from a common algal ancestor.

• Ancestry Debate: Specific ancestor (Mesostigmatales or Charales?) is debated.

• Common Ancestor: DNA suggests all plants arose from a single green algae species, possibly categorized under the kingdom Viridiplantae.

Kingdom Classification

• Viridiplantae: Includes land plants and green algae; excludes red and brown algae.

  • Clades: 1) Chlorophytes (never made it to land), 2) Charophytes (did adaptation to land).

Plant Characteristics

• Eukaryotic: Cells with a nucleus.

• Multicellular: Made of multiple cells.

• Autotrophic: Capable of photosynthesis.

• Embryo Protection: Retain and nourish embryos.

• Adaptations for Land: Includes vascular tissues for nutrient and water dispersion.

• Plant Groups:

  • Vascular Plants: Have conducting tissues for water/nutrient transport.

  • Nonvascular Plants: Lack these conducting tissues.

Four Major Plant Groups

1. Nonvascular Plants: Mosses, liverworts, hornworts.

2. Seedless Vascular Plants: Club mosses, ferns, horsetails.

3. Gymnosperms: Conifers, cycads, gnetophytes, ginkgo.

4. Angiosperms: Flowering plants.

Terrestrial Adaptations

• Waxy Cuticle Development: Helps prevent water loss in dry environments.

• Stomata: Small openings for gas exchange that solve water retention issues.

• Alternation of Generations: Evolution from dominant gametophyte in algae to sporophyte in most modern plants.

• Vascularization: Allowed plants to grow taller in search of sunlight while still accessing water.

• Woody Tissue: Lignin provides support, enabling taller growth.

Plant Life Cycle

• Haplodiplontic life cycle: Alternation of multicellular diploid (sporophyte) and haploid (gametophyte) stages.

  • Spores: Formed by sporophyte via meiosis, give rise to gametophytes.

  • Gametophytes: Produce gametes through mitosis that fuse to form zygotes, initiating the sporophyte generation.

Nonvascular Plants: Bryophytes

• Bryophytes: Primitive nonvascular plants consisting of mosses, liverworts, and hornworts.

  • Characteristics: Lacking vascular systems, typically short (�30 cm).

  • Sporophyte Generation: Inconspicuous; gametophyte is dominant and photosynthetic.

  • Reproductive Methods: Require moisture for motile sperm to fertilize eggs.

Typical Moss Life Cycle

• Dominant Gametophyte: Nutritionally dependent sporophyte; requires water for sperm mobility.

• Gametophytes: Structure includes antheridia (male) and archegonia (female).

• The cycle alternates between the production of gametes and spores.

Liverworts

• Division Hepaticophyta: Ancient plants similar to mosses, often found in moist environments.

  • Reproductive Similarities: Share characteristics with mosses, inconspicuous sporophytes.

Hornworts

• Division Anthocerotophyta: Characterized by long, narrow sporophytes; photosynthetic.

  • Unique Feature: Single large chloroplast per cell.

Vascular Plants

• Characteristics: Specialized cells forming xylem and phloem.

• Types: Include seedless vascular plants like ferns and their allies, which utilize motile sperm for reproduction.

Seedless Vascular Plants

• Division Pterophyta: Ferns and allies, exploiting vascularization for height and nutrient transport.

  • Dominant Generation: Sporophyte generation, reproduction using spores.

Homosporous vs. Heterosporous

• Homosporous: Produce single type of spores, leading to bisexual gametophytes.

• Heterosporous: Produce distinct male and female gametophytes (e.g., seed plants).

Gymnosperms

• Characteristics: Exposed seeds, lack flowers and fruits.

  • Divisions: Include coniferophyta, cycadophyta, gnetophyta, and ginkgophyta.

Angiosperms (Flowering Plants)

• Dominant Plant Group: Features include flowers and fruits, enhancing reproductive efficiency.

• Types: Classified into monocots and eudicots, each with distinct characteristics.

Angiosperm Life Cycle

• Pollen Transfer: From anther to stigma; double fertilization results in triploid endosperm tissue nourishing the embryo.

• Seed Development: Leads to the next sporophyte generation released in a seed.