gymnosperm

Examples of gymnosperm in the following topics:

• Characteristics of Gymnosperms

  • Gymnosperms are seed plants that have evolved cones to carry their reproductive structures.
  • The name gymnosperm means "naked seed," which is the major distinguishing factor between gymnosperms and angiosperms, the two distinct subgroups of seed plants.
  • Gymnosperms are older than angiosperms on the evolutionary scale.
  • Gymnosperms are sporophytes (a plant with two copies of its genetic material, capable of producing spores).
  • It is important to note that the seeds of gymnosperms are not enclosed in their final state upon the cone.

• Evolution of Gymnosperms

  • Seed ferns gave rise to the gymnosperms during the Devonian Period, allowing them to adapt to dry conditions.
  • The Ginkgoales, a group of gymnosperms with only one surviving species, the Gingko biloba, were the first gymnosperms to appear during the lower Jurassic.
  • Gymnosperms expanded in the Mesozoic era (about 240 million years ago), supplanting ferns in the landscape, and reaching their greatest diversity during this time.
  • The Jurassic period was as much the age of the cycads (palm-tree-like gymnosperms) as the age of the dinosaurs.
  • Explain how and why gymnosperms became the dominant plant group during the Permian period

• Sexual Reproduction in Gymnosperms

  • Gymnosperms produce both male and female gametophytes on separate cones and rely on wind for pollination.
  • As with angiosperms, the life cycle of gymnosperms is also characterized by alternation of generations.
  • Gymnosperm reproduction differs from that of angiosperms in several ways.
  • Double fertilization is a key event in the life cycle of angiosperms, but is completely absent in gymnosperms.
  • These series of micrographs shows male and female gymnosperm gametophytes.

• Diversity of Gymnosperms

  • Gymnosperms are a diverse group of plants the protect their seeds with cones and do not produce flowers or fruits.
  • Modern gymnosperms are classified into four phyla.
  • Conifers are the dominant phylum of gymnosperms, with the most variety of species .
  • Cycads bear large cones and may be pollinated by beetles rather than wind, which is unusual for a gymnosperm ().
  • Like angiosperms, but unlike other gymnosperms, all gnetophytes possess vessel elements in their xylem.

• Life Cycle of a Conifer

  • Like all gymnosperms, pines are heterosporous, generating two different types of spores: male microspores and female megaspores.

• The Major Divisions of Land Plants

  • Seed-producing plants include gymnosperms, most notably conifers, which produce "naked seeds," and the most successful of all modern-day plants, angiosperms, which are the flowering plants.

• Evolution of Angiosperms

  • Rather than being derived from gymnosperms, angiosperms form a sister clade (a species and its descendents) that developed in parallel with the gymnosperms.

• The Evolution of Seed Plants and Adaptations for Land

  • The sperm of modern gymnosperms lack flagella, but in cycads and the Gingko, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.

• Pollination and Fertilization

  • In gymnosperms, pollination involves pollen transfer from the male cone to the female cone.

• Development of the Seed

  • In gymnosperms, the two sperm cells transferred from the pollen do not develop seed by double fertilization, but one sperm nucleus unites with the egg nucleus and the other sperm is not used.