Gymnosperms

Plants with seed-cones

Gymnosperms are vascular plants with seeds, usually inside cones, and consist of four living groups (Cycads, Ginkgo, Conifers, and Gnetophytes), as well as many extinct groups. They are called gymnosperms, because they have "naked seeds" (gymno-sperms) which means that their seeds are not protected inside an ovary, like the angiosperms. More specifically, in gymnosperms, pollination occurs when pollen comes in direct contact with the ovule (n.b. pollen in angiosperms never tocuhes the ovules). Depending on the study, some researchers claim that they are a paraphyletic grade, where other studies show them being a monophyletic grouping. Evolutionary biologists have named the clade spermatophytes, which are seed plants that include all gymnosperms and the angiosperms. The gymnosperms, and specifically the conifers, consist of the largest single (non-clonal) organisms on Earth (i.e. Sequoiadendron giganteum) and the oldest single (non-clonal) organisms on Earth (i.e. Pinus longaeva)

Above: the cycad Cycas (left); the only living ginkgophyte Ginkgo (middle); the female cones of a conifer, the spruce Picea (right)

Seed-bearing phase (=sporophyte)

  • This phase is dominant, multicellular, and photosynthetic

Vegetative features

Stems: highly variable

Leaves: highly variable

  • Possess true leaves (=megaphylls)

  • Many are evergreen, but not all (e.g. Larix, Taxodium)

  • Leaf variety in living forms

    • Mostly needle-like, scale-like, or awl-like in conifers

    • Compound in cycads and some conifers

    • Fan-shaped in Ginkgo

    • Angiosperm-like in Gnetum and Welwitschia

    • Loss of leaves is a secondary adaptation in Ephedra

Roots

  • Roots present; extremely long in desert members

  • Secondary growth in most members

Reproductive features

  • Seeds usually found in cones, except Ginkgo

  • Cones consist of either modified leaves (=simple cones, e.g. cycad cone), or modified stems (=compound cones, e.g. female pine cone)

  • All members are heterosporous (i.e. 2 different types of "spores" - pollen grains and megaspores in seeds)

    • Meiosis creates a mega-spore found in ovules/seeds

      • **Ovule is a "female" sporangium with a seed coat (=integument), with 1 megaspore inside

    • Meiosis creates micro-spores which are pollen grains

      • **Pollen sac is a "male" sporangium that produces micro-spores (=pollen)

Gamete-bearing phase (=gametophyte)

    • Tiny, multicellular, and the female gametophyte is dependent on the sporophyte

    • Gymnosperm gametophytes are not photosynthetic

    • Female gametophyte found inside the megaspore, which is inside the ovule/seed (not free-living)

    • Male gametophyte is found inside the pollen grain (= a microspore)

Diversity

  • The gymnosperms are a paraphyletic grade of plants with seed-cones (if including fossil taxa). Living gymnosperms are represented by four living groups:

  1. Cycads

  2. Ginkgo

  3. Conifers

  4. Gnetophytes

  • This page includes the complete list of extinct and living gymnosperms

Classification

└Embryophytes

└Tracheophytes

└Euphyllophytes

└Lignophytes

└Spermatophytes (except angiosperms)

Geologic Age

Questions for Thought

  • What features do all "gymnosperms" exhibit?

  • What is the synapomorphy for the lignophytes?

  • What attributes characterize a cycad?

  • How is a cycad different looking than a palm?

  • How are the gnetophytes similar and different to angiosperms?

  • What features of Ginkgo are considered derived for a gymnosperm?

  • What aspects of a conifer's life cycle are different from a fern?

  • What adaptations do conifers possess to survive cold and dry environments?

Additional Resources