What is the function of gymnosperms?
• The word Gymnosperm was first used by Theophrastus (300 BC) in his book “Inquiry into Plants” to embrace the plants with unprotected seeds. Gymnosperms (Gk gymnos: naked, spemia, seed) are naked seeded plants with their ovules freely exposed on open megasporophylls. Goebel (1887) has rightly described them as “phanerogams without ovary”.For More Biology Doubts visit main page of Physics Wallah.
• Gymnosperms are the most ancient seed plants that originated during the late Paleozoic era (265 million years ago), but flourished well during the Mesozoic era. The Jurassic period perhaps was the best time for gymnosperms.
• 200 million years ago the earth was dominated by the flora of gymnosperms. Gradully the members of gymnosperms disappeared and replaced by angiosperms with changing time and climatic conditions.
• Living gymnosperms are spread over 70 genera and 725 species. Bold (1963) has reported only 722 species of present day gymnosperms. Of these, some 50 genera and 500 species belong to conifers. About 16 genera and 53 species of living gymnosperms have been reported from India.
• The living gymnosperms are widely distributed in the cold climates. Cycads occurs in tropical and subtropical areas.
• In India, mostly the conifers thrive well in hilly areas. Very few gymnosperms grow in plains.
• A number of gymnosperms are now growing as omamentals, e.g., Thuja, Arauearia (native of South America), Ginkgo.
• Gymnosperms are predominatly woody plants represented by trees, shrubs (e.g., Ephedra) or rarely climbers.
• The main plant body is sporophyte (2n) and is well differentiated into root, stem and leaves.
• Plants possess taproot. In some cases roots show symbiosis with certain blue green algal cells, e.g., coralloid roots of Cycas (e.g. Anabaena cycadae and Nostoc or with fungus, e.g., mycorrhizal roots of Pinus, Arauearia, etc.
• Stems are erect, branched (unbranched in most species of Cycas) and woody. Leaf scars show their characteristic presence on the stem.
• Leaves may be of one kind, i.e., monomorphic; or of two kinds, i.e., dimorphic:
• Foligae leaves that are all invariably evergreen may be simple or compound
• Scale leaves are minute and deciduous
• The leaves may be few, large and pinnately compound as in Cycas, numerous, small, simple and needle shaped as in Pinus or reduced and scaly as in Ephedra.