Gymnosperms are flowerless plants that produce cones and seeds. The term gymnosperm comes from the composite word in Greek means “naked seed,” as gymnosperm seeds are not encased within an ovary. Rather, they sit exposed on the surface of leaf-like structures called bracts. Gymnosperms are vascular plants of the subkingdom Embyophyta and include conifers, cycads, ginkgoes, and gnetophytes.
Taxonomists recognize four types of gymnospermous plants, They are Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta. With 88 genera and more than 1,000 species distributed throughout the world. Gymnosperms are plants in which the ovules are not enclosed within the ovary wall, unlike the angiosperms. It remains exposed before and after fertilization, and before developing into a seed. The stem of gymnosperms can be branched or unbranched. The thick cuticle, needle-like leaves, and sunken stomata reduce the rate of water loss in these plants.
Characteristics of Gymnosperms
Following are the important characteristics of gymnosperms:
- They do not produce flowers.
- Seeds are not formed inside a fruit. They are naked.
- They are found in colder regions where snowfall occurs.
- They develop needle-like leaves.
- They are perennial or woody, forming trees or bushes.
- They are not differentiated into an ovary, style, and stigma.
- Since stigma is absent, they are pollinated directly by the wind.
- The male gametophytes produce two gametes, but only one of them is functional.
- They form cones with reproductive structures.
- The seeds contain endosperm that stores food for the growth and development of the plant.
- These plants have vascular tissues that help in the transportation of nutrients and water.
- Xylem does not have vessels, and the phloem has no companion cells and sieve tubes.
Life Cycle of Gymnosperms
The life cycle of gymnosperms is both haploid and diploid, i.e., they reproduce through the alternation of generations. They have a sporophyte-dominant cycle. The gametophyte phase is relatively short. The reproductive organs are usually cones.
Male Cones: These have microsporophylls that contain microsporangia. Microsporangia produces haploid microspores. Few microspores develop into male gametes called pollen grains, and the rest degenerate.
Female Cones: The megasporophylls cluster together to form female cones. They possess ovules containing megasporangium. It produces haploid megaspores and a megaspore mother cell.
The pollen reaches the egg through wind or any other pollinating agent, and the pollen grain releases a sperm. The nuclei of male and female gametophytes fuse to form a zygote. This is known as fertilization. The seed appears as scales that can be seen on the cones of the gymnosperm.
These are the following examples of gymnosperms: