Gymnosperms

• Seeds changed the course of plant evolution, enabling their bearers to become the dominant producers in most terrestrial ecosystems
• Seed plants originated about 360 million years ago
• Seed


  An embryo and nutrients surrounded by a protective coat
• Seeds can disperse over long distances by wind or other means
• Seed plants


  • Reduced gametophytes
  • Heterospory
  • Ovules
  • Pollen
• Reduced gametophytes


  The gametophytes of seed plants develop within the walls of spores that are retained within tissues of the parent sporophyte
• Plant groups

  • Nonvascular plants (bryophytes)
  • Seedless vascular plants
  • Gymnosperms
  • Angiosperms
• Gymnosperms


  • Miniaturization of their gametophytes
  • Development of seeds from fertilized ovules
  • Transfer of sperm to ovules by pollen
• Pine life cycle


  1. Sporophyte produces sporangia in male and female cones

  2. Microspores called pollen grains contain male gametophytes

  3. Megaspores develop into female gametophytes

  4. Takes nearly three years from cone production to mature seed

  
• Gymnosperms were better suited than nonvascular plants to drier conditions
• Gymnosperms served as food for herbivorous dinosaurs
• Gymnosperms were pollinated by insects over 100 million years ago
• Angiosperms began to replace gymnosperms near the end of the Mesozoic
• Gymnosperm phyla

  • Cycadophyta (cycads)
  • Gingkophyta (Ginkgo biloba)
  • Gnetophyta (Gnetum, Ephedra, Welwitschia)
  • Coniferophyta (conifers)
• Cycads


  • Have large cones and palmlike leaves
  • Have flagellated sperm
• Ginkgo biloba


  • Has flagellated sperm
  • Has a high tolerance to air pollution
  • Is a popular ornamental tree
• Angiosperms now dominate more terrestrial ecosystems, though conifers still dominate in some regions including the northern latitudes
• The gymnosperms consist of four phyla


  • Cycadophyta (cycads)
  • Gingkophyta (one living species: Ginkgo biloba)
  • Gnetophyta (three genera: Gnetum, Ephedra, Welwitschia)
  • Coniferophyta (conifers, such as pine, fir, and redwood)
• Phylum Cycadophyta


  • Individuals have large cones and palmlike leaves
  • Unlike most seed plants, cycads have flagellated sperm
  • These thrived during the Mesozoic, but most of the few surviving species are endangered
• Phylum Ginkgophyta


  • This phylum consists of a single living species, Ginkgo biloba
  • Like the cycads, this group also has flagellated sperm
  • It has a high tolerance to air pollution and is a popular ornamental tree
• Phylum Gnetophyta


  • This phylum comprises three genera: Gnetum, Ephedra, and Welwitschia
  • Species vary in appearance, and some are tropical whereas others live in deserts
• Phylum Gnetophyta

  • Welwitschia
  • Gnetum
  • Ephedra
• Phylum Coniferophyta


  • This phylum is the largest of the gymnosperm phyla
  • Most conifers are evergreens and can carry out photosynthesis year round
• Angiosperms are seed plants with reproductive structures called flowers and fruits
• Angiosperms are the most widespread and diverse of all plants
• Anthophyta


  The phylum that all angiosperms are classified in, from the Greek anthos for flower
• Angiosperms have two key adaptations

  • Flowers
  • Fruits
• Flower


  An angiosperm structure specialized for sexual reproduction
• Many species are pollinated by insects or animals, while some species are wind-pollinated
• Floral organs

  • Sepals
  • Petals
  • Stamens
  • Carpels
• Stamen


  Consists of a stalk called a filament, with a sac called an anther where the pollen is produced
• Carpel


  Consists of an ovary at the base and a style leading up to a stigma, where pollen is received
• Flowers that have all four organs are called complete flowers, those lacking one or more organs are called incomplete flowers
• Radial symmetry


  Any imaginary line through the central axis divides the flower into two equal parts
• Bilateral symmetry


  A flower can only be divided into two equal parts by a single imaginary line
• Most species have flowers with both functional stamens and carpels, but in some species they occur on separate flowers
• Fruit


  Formed when the ovary wall thickens and matures, protects seeds and aids in their dispersal
• Fruits


  • Tomato
  • Ruby grapefruit
  • Nectarine
  • Hazelnut
  • Milkweed
• Fruit adaptations


  • Seeds can be carried by wind, water, or animals to new locations
• Mechanisms that disperse seeds

  • Explosive action
  • Wings
  • Berries and other edible fruits
  • Barbs