Division : Gymnospermae (Gymnos = naked; sperma = seed)
Gymnosperms are the plants with naked seeds. They include simple members of the Phanerogamae (Spermatophyta) and are also described as 'Phanerogams without ovary'.
The term "Gymnosperm" was first used by Theophrastus in 300 B.C. in his book "Enquiry into plants". There are about 70 genera and 725 living species of Gymnosperms. In India it is represented by 16 genera and 53 species.
Most of the Gymnosperms are evergreen, perennial woody trees or shrubs. They are vascular plants having xylem with tracheids and phloem with sieve cells. They are non-flowering plants producing naked seeds. (fruits are not produced).
The Gymnosperms show heteromorphic alternation of generations. The sporophyte is diploid, dominant, autotrophic, independent while the gametophyte is haploid, recessive and dependent. (It us much reduced and exits within sporophyte).
The plant body i.e. sporophyte is differentiated into root, stem and leaves. The root system is well developed tap root system. Coralloid roots of Cycas show association with blue-green algae and roots of Pinus show association with endophytic fungi called mycorrhizae.
The gymnospermic stem is mostly erect, aerial, solid and cylindrical. In Cycas it is usually unbranched, while in conifers it is branched. The leaves are dimorphic. The foliage leaves are green, simple, needle like or pinnately compound, where as scale leaves are small, membranous and brown.
Secondary growth is seen in Gymnosperms due to presence of cambium.
Gymnosperms are heterosporous. They produce microspores (pollen grains) in microsporangia and megaspores in megasporangia (ovules). The sporangia are borne on leafy structures called sporophylls which are often aggregated to form cones or strobilli (singular-strobillus).
The pollination in Gymnosperm is anemophilous (wind pollination) and direct as the pollen grains are received directly in the pollen chamber of the ovule. Fertilization is achieved through a pollen tube. This process is called siphonogamy. Vegetative reproduction takes place with the help of bulbils.
Examples : Cycas, Pinus, Ginkgo.
Some Gymnosperms like Ginkgo biloba are called living fossils. It is because the plant is found in living as well as fossil form and the number of fossil forms is much more than the living forms.
Gymnosperms vary in their size e.g. Sequoia sempervirens is the tallest living plant in the world. It is commonly called coast redwood of California. The height of the plant is 366 feet. Taxodium mucronatum has a girth of about 125 feet. Zamia pygmaea is the smallest gymnosperms and is about 25 cm only.