Chapter 30: Plant Diversity II: The Evolution of Seed Plants

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

Adaptations: Seed Plants Gametophytes are even more reduced. Seeds replaced spores as the means for dispersal. Pollen is the vehicle for sperm cells.

Life Cycle switch

Gymnosperms - Divisions Coniferophyta - Conifers Cycadophyta - Cycads Ginkgophyta - Ginkgo Gnetophyta - Gnetae ~700 species

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

Life Cycle Most are heterosporous. Male gametophyte = pollen grain. Multi-cellular female gametophyte still produces archegonia.

Conifers Two types of cones  Pollen cone - male  Ovulate cone - female

Pollen Cone Male Cones Sporangia

Pollen Cone Sporangia with pollen Male Gametophyte or Pollen

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

Ovulate Cone At time of Pollination Ovulate Cone

Megaspore Mature Cones

Conifers Fertilization Fusion of sperm and egg to produce a zygote. Pollination and fertilization may be separated by 1 year.

Conifer Seeds Embryo Mature Seed

Importances Coniferophyta:  Lumber  Paper  Resins

Importances  Food  Landscaping  Christmas trees

Other Examples Cypress Pacific Yew

Importances Cycadophyta:  Landscaping  Food

Ginkgo Ginkgophyta:  1 species extant  Living fossil

Ginkgo Tree Fall Color

Ginkgo - Male Male cones Sperm

Ginkgo - Female Female cones Mature cones

Importances Landscaping Drug Seeds (?)

Importances Gnetophyta:  "Mixed bag" of species  Various importances Ephedra

Other Gnetophyta Welwitschia Gnetum

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

Characteristics Have seeds, flowers and fruits.

Characteristics Xylem may have vessels.

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

Importances Food Lumber Medicines Landscaping Fibers

Importances Rubber Flower Industry Dyes Spices Soil Erosion Control

Angiosperms Main group for study of plants in future lessons.

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