Chapter 18: Plants and Fungi

Origins of Plants

  • Multicellular, photosynthetic, sessile, eukaryotic
  • Ancestors: aquatic protists → land at ≈475 mya\approx 475\,\text{mya}

Early Land Adaptations

  • Challenges: gravity & desiccation
    • Gravity → low, ground-hugging forms
    • Desiccation → waxy cuticle
  • Later: vascular tissues (xylem & phloem) give transport + structural support

Plant Groups Overview

  • Non-vascular plants (mosses)
  • Vascular seedless plants (ferns, horsetails)
  • Gymnosperms (seed, no flower)
  • Angiosperms (seed + flower/fruit)

Non-Vascular Plants

  • No roots/vascular tissue; reproduce by spores
  • Require saturated habitats; remain very small

Vascular Tissue & Seedless Plants

  • Xylem: water; Phloem: sugars
  • Secondary role: strength → vertical growth, wind resistance
  • Ferns & allies: roots + vessels, spore reproduction, need wet sites

Seeds & Vascular Seed Plants

  • Seed = embryo + nutrient/water supply + protective coat
    • Survive dormancy, drought, cold; enable wider colonization
  • Two lineages: Gymnosperms & Angiosperms

Gymnosperms

  • Cones for reproduction; wind pollinated
  • Secondary growth → bark, height, longevity (e.g., Bristlecone >5000 y)
  • Examples: pines, cycads, cedars, bald cypress

Angiosperms

  • Flowers (animal or wind pollinated) + fruits (seed dispersal)
  • Currently the dominant and most diverse plant group
  • Include grasses, broad-leaf trees, all major food crops

Flower Structure & Pollination

  • Stamen (anther + filament) → pollen
  • Carpel (stigma, style, ovary) → ovules/seeds
  • Pollination = pollen to stigma; often rewarded (nectar, pollen)

Seed Dispersal

  • Reduces parent-offspring competition; may include fertilization bonus
  • Mechanisms: animal ingestion, hitchhiking, wind, water

Fungi Basics

  • Closer to animals than plants; heterotrophic decomposers, symbionts, parasites
  • Grow through food source; cell walls of chitin
  • Can cause plant diseases, building molds, toxic mushrooms

Fungi–Plant Interactions

  • Mycorrhizae: fungus exchanges soil NN & PP for plant sugars
  • Essential for nutrient uptake; analogous to gut microbes in animals