In this article we will discuss about Gymnosperms:- 1. Meaning of Gymnosperms 2. Distinguishing Features of Gymnosperms.
Meaning of Gymnosperms:
“Phanerogams without an ovary” have been referred as Gymnosperms (Gymnos, naked; sperma, seed) or naked-seeded plants by Goebel. The lower Gymnosperms, such as members of Cycadales resemble with the higher Cryptogams (Pteridophytes), while the higher Gymnosperms such as Gnetales and Coniferales, resemble with members of Angiosperms.
This sub-division of Phanerogams (flowering plants), i.e., Gymnosperms, is represented by over 60 genera and 700 species, of which about 16 genera and 53 species have been reported from India.
Distinguishing Features of Gymnosperms:
1. Plants are woody perennials with shruby or treelike habit and show xerophytic characters.
2. Some of the members attain a height of more than 100 meters, e.g., Sequoiadendron giganteum.
3. Plant body is differentiated into roots, stem and leaves.
4. Tap root system is exarch and diarch to polyarch.
5. Leaves are of two types-foliage leaves and scaly leaves. They are pinnately compound as in Cycas or needle-like as in Pinus.
6. The vascular bundles in stem are conjoint, collateral, open and endarch.
7. Due to the presence and activity of cambium, secondary growth is present.
8. The wood becomes closely packed or pycnoxylic in conifers due to the much reduced nature of pith and cortex. It is manoxylic or loose in Cycas due to the presence of well-developed pith and cortex.
9. The xylem is composed of tracheids with bordered pits.
10. In phloem, companion cells are absent.
11. The reproductive parts are generally arranged in the form of compact and hard cones or strobili. The cones are generally unisexual.
12. In male cones, many microsporophylls are arranged on the central axis, each having many microsporangia containing microspores or pollen grains.
13. The ovules are covered by a single integument and are orthotropous. The integument consists of an outer fleshy, a middle stony and inner fleshy layer. It surrounds the nucellus.
14. Each ovule opens with the help of a mouth opening or micropyle.
15. Formation of embryo is meroblastic, i. e., develops from a small part of zygote.
16. Polyembryony is present in many members, e.g., Pinus.
17. True fruits are lacking.
18. Plants show alternation of generations.
19. Members of most of the orders (Cycadales, Coniferales and Ginkgoales) are living while that of the other orders like Cordaitales and Cycadeoideales are represented by fossil genera.