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Learning Goals & Outcomes

  • Goal: Understand key evolutionary traits of seed plants (gymnosperms and angiosperms)
  • Outcomes:
    • Describe features/advantages of seed plants: seeds, reduced gametophytes, heterospory, ovules, and pollen
    • Distinguish between gymnosperms and angiosperms and between monocots and eudicots

Traits Common to All Seed Plants

  • Seeds: Embryo and nutrients within a protective coat
  • Reduced Gametophytes: Microscopic size, dependent on sporophyte for nutrition
  • Heterospory: Production of two different types of spores
  • Ovules: Structure containing the female gametophyte
  • Pollen: Contains male gametophytes

Advantages of Seeds

  • Structure: Embryo + nutrients + protective coat
  • Adaptations:
    • Stored food supply, can remain dormant until conditions are favorable for germination
    • No need for water for fertilization – reproduction under a wider range of conditions
    • Long-distance dispersal by wind or animals

Advantages of Reduced Gametophytes

  • Seed plant gametophytes are microscopic, allowing them to develop within the sporophyte's sporangia:
    • Protects against environmental stresses
    • Enables nutrient uptake from parental sporophyte

Gametophyte-Sporophyte Relationships

  • Mosses:
    • Independent, photosynthetic gametophytes
  • Seed Plants:
    • Reduced, dependent gametophytes
  • Gymnosperms: Microscopic female gametophytes in ovulate cones
  • Angiosperms: Microscopic female/male gametophytes in flowers

Heterospory

  • Heterosporous Seed Plants:
    • Megasporangia: Produce megaspores (female gametophytes)
    • Microsporangia: Produce microspores (male gametophytes/pollen grains)

Ovules and Production of Eggs

  • Ovule Structure:
    • Composed of megasporangium, megaspore, protective integuments
    • Gymnosperms: One integument
    • Angiosperms: Usually two integuments

Pollen and Production of Sperm

  • Pollen Formation: Microspores develop into pollen grains containing male gametophytes
  • Advantages: Eliminates need for water film and can be dispersed by air or animals

Living Seed Plants

  • Clades:
    • Gymnosperms
    • Angiosperms
  • Reproductive Structures:
    • Gymnosperms: Exposed seeds on sporophylls forming cones
    • Angiosperms: Seeds in fruits (mature ovaries)

Gymnosperms

  • Known as “naked seeds”
  • Seed exposure on modified leaves forming cones
  • Predominantly cone-bearing plants (conifers): Pines, firs, redwoods

Angiosperms

  • Most diverse and widespread plant group
  • Reproductive structures:
    • Flowers: Specialized for sexual reproduction with modified leaves
      • Sepals: Enclose unopened flowers
      • Petals: Attract pollinators
      • Stamens: Male organs, produce pollen
      • Carpels: Female organs, produce ovules

Fruits

  • Form from maturing ovary walls
  • Functions: Protect seeds and facilitate dispersal
  • Types of fruits:
    • Fleshy Fruits: e.g., tomatoes, nectarines
    • Dry Fruits: e.g., hazelnuts

Seed Dispersal Mechanisms

  • Seeds dispersed by:
    • Wind (explosive action)
    • Water
    • Animals (edible fruits, barbs)

Angiosperm Diversity

  • Over 250,000 living species
  • Traditionally two groups: Monocots and Eudicots
  • Monocots: One cotyledon, parallel leaf venation, fibrous root systems
  • Eudicots: Two cotyledons, netlike venation, taproot systems

Characteristics of Monocots vs Eudicots

  • Monocots:

    • One cotyledon
    • Vascular tissue scattered in stems
    • Pollen with one opening
    • Floral organs usually in multiples of three

  • Eudicots:

    • Two cotyledons
    • Vascular tissue arranged in a ring
    • Pollen with three openings
    • Floral organs typically in multiples of four or five

Ecological and Economic Importance

  • Monocots:
    • This group includes grasses, orchids, palms
  • Eudicots:
    • Contains significant families like legumes (e.g., peas) and rose family (e.g., roses)
  • Dominance: Over two-thirds of angiosperm species are eudicots.