Plant Diversity II: The Evolution of Seed Plants

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Chapter 30

• Plant Diversity IIThe Evolution of Seed Plants

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Seed Plants

• Gymnosperms naked seeds
• Angiosperms covered seeds
• These two groups are the dominant plants on Earth
  today.

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Adaptations Seed Plants

• Gametophytes are even more reduced.
• Seeds replaced spores as the means for dispersal.
• Pollen is the vehicle for sperm cells.

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Life Cycle switch
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Gymnosperms - Divisions

• Coniferophyta - Conifers
• Cycadophyta - Cycads
• Ginkgophyta - Ginkgo
• Gnetophyta - Gnetae
• 700 species

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Characteristics

• Seeds with multiple seed leaves.
• Cones (strobili).
• Xylem with tracheids only.
• No flowers or fruits.

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Life Cycle

• Most are heterosporous.
• Male gametophyte pollen grain.
• Multi-cellular female gametophyte still produces
  archegonia.

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Conifers

• Two types of cones
• Pollen cone - male
• Ovulate cone - female

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Pollen Cone

• Male Cones

• Sporangia

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Pollen Cone

• Sporangia with pollen

• Male Gametophyte or Pollen

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Pollination

• Transfer of pollen from one individual to
  another.
• Usually accomplished by the wind for most
  Gymnosperms.

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Ovulate Cone

• At time of Pollination

• Ovulate Cone

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Ovulate Cone

• Megaspore

• Mature Cones

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Fertilization

• Fusion of sperm and egg to produce a zygote.

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Conifers

• Pollination and fertilization may be separated by
  1 year.

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Conifer Seeds

• Embryo

• Mature Seed

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Importances

• Coniferophyta
• Lumber
• Paper
• Resins

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Importances

• Food
• Landscaping
• Christmas trees

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Other Examples

• Cypress

• Pacific Yew

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Importances

• Cycadophyta
• Landscaping
• Food

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Ginkgo

• Ginkgophyta
• 1 species extant
• Living fossil

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Ginkgo

• Tree

• Fall Color

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Ginkgo - Male

• Male cones

• Sperm

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Ginkgo - Female

• Female cones

• Mature cones

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Importances

• Landscaping
• Drug
• Seeds (?)

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Importances

• Gnetophyta
• "Mixed bag" of species
• Various importances

• Ephedra

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Other Gnetophyta

• Welwitschia

• Gnetum

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Angiosperms

• Division - Anthophyta
• Most dominant plant group on land.
• Two main classes
• Monocotyledones (Monocots)
• Dicotyledones (Dicots)
• 235,000 species

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Characteristics

• Have seeds, flowers and fruits.

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Characteristics

• Xylem may have vessels.

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Life History

• Male gametophyte reduced to a 2-3 celled pollen
  grain.
• Female gametophyte reduced to an embryo sac.
• Double fertilization.

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Importances

• Food
• Lumber
• Medicines
• Landscaping
• Fibers

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Importances

• Rubber
• Flower Industry
• Dyes
• Spices
• Soil Erosion Control

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Angiosperms

• Main group for study of plants in future lessons.

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Summary

• Know the adaptations of seed plants.
• Know examples, life cycles, and importances of
  the gymnosperms and angiosperms.