Gymnosperms represent a primitive group of seed bearing plant (Spermotophytes) in which the seeds are naked i.e. they are not covered by the fruit wall as in Angiosperms (the word Gymnos means naked and spermos means seed).
Salient features of Gymnosperms
Gymnosperms represent a primitive group of seed bearing plant (Spermotophytes) in which the seeds are naked i.e. they are not covered by the fruit wall as in Angiosperms (the word Gymnos means naked and spermos means seed). This is because in Gymnosperms the ovules are exposed and they are not covered by ovary. Instead the ovules are borne directly on open carpellary leaves called megasporophylls and hence they are naked and they develop into naked seeds after fertilization.
Gymnosperms were most abundant during the Mesozoic era (225 million years) ago. However, they form only a small part of the present day vegetation. There are about 70 genera and 900 species of gymnosperms distributed in tropical and temperate regions. Most of them are Conifers mostly evergreen, with needle like leaves. They are found in the form of coniferous forests in the Himalayas in the Indian sub-continent. The common conifers are species of pine, fir, spruce,Cedar,Cupressus, Sequoia gigantia, (red wood tree which measures more than 100 meters in height).
Distinguishing features of Gymnosperms
Gymnosperms are woody perennial which are mainly trees and rarely shrubs.
The life cycle of gymnosperms shows heteromorphic alternation of generations.
They form an intermediate group between pteridophytes and Angiosperms i.e they are more advanced than pteridophytes but are primitive than angiosperms. The plant body is the sporophyte (diploid) mostly a tree with well developed roots, stem and leaves.
The sporophyte bears two types of fertile leaves, the microsporophyll that produces microspores and megasporophyll that produces megaspores. Mostly the spores are grouped into compact cones or strobili. Spores on germination develop into gametophytes which are very much reduced, microscopic and dependent on sporophyte. Ovules are naked.
Pollination is mostly by wind (anemophilous). Fertilization involves only one fusion. Female gametophyte provides nutrition to the developing embryo. The endosperm (female gametophyte) is a pre-fertilization tissue and is haploid.sac) and the embryo (of the next sporophyte generation). All the nutrients for life are supplied Seeds are naked and not embedded in fruit.
Vessels are absent in xylem (except Gnetales)
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