Gymnosperms

• Gymnosperms


  Plants in which the ovules are not enclosed by any ovary wall and remain exposed, both before and after fertilisation
• Gymnosperms


  • Include medium-sized trees or tall trees and shrubs
  • Have tap roots
  • Some have fungal association in the form of mycorrhiza
  • Some have small specialised roots called coralloid roots associated with N2-fixing cyanobacteria
  • Have unbranched (Cycas) or branched (Pinus, Cedrus) stems
  • Have simple or compound leaves
  • Leaves are well-adapted to withstand extremes of temperature, humidity and wind
  • Conifers have needle-like leaves that reduce surface area
  • Conifers have thick cuticle and sunken stomata to reduce water loss
  • Cycas has pinnate leaves that persist for a few years
• Heterosporous

  Produce haploid microspores and megaspores
• Reproduction in gymnosperms

  1. Sporophylls bear sporangia in which spores are produced

  2. Microsporophylls bear microsporangia that produce microspores which develop into male gametophyte (pollen grain)

  3. Megasporophylls bear ovules containing megaspore mother cell that divides meiotically to form 4 megaspores, one of which develops into female gametophyte bearing archegonia

  4. Pollen grains are carried by air currents and reach the ovules, pollen tube grows towards archegonia and discharges male gametes

  5. Fertilisation occurs, zygote develops into embryo and ovules develop into seeds
• Types of gymnosperms


  • Cycas
  • Pinus
  • Cedrus
• Cycas and Pinus are dioecious and monoecious respectively
• Gymnosperms are ancient plants having seeds but lacking flowers and belong to the plant division Pinophyta
• Gymnosperms have a diploid sporophyte as the dominant plant body and a reduced, dependent gametophyte
• Gymnosperms have true roots, stems and leaves
• Gymnosperms have a life cycle with alternation of generations, with independent sporophyte and dependent gametophyte generations
• Sequoia is the giant redwood tree, one of the tallest tree species
• The seed is borne on the surface of the plant, usually attached to cones or strobili.
• Gymnosperm seeds are not enclosed within an ovary.
• Conifers include pine trees, fir trees, cedars, cypresses, junipers, larches, sequoias, and spruces.
• Ginkgo biloba is a living fossil from the Mesozoic era and has fan-shaped leaves.
• Cycas

  Dioecious
• Pinus


  Monoecious