Characteristics, life cycle, economic significance

1. Introduction

1. Gymnosperms are seed-producing plants where seeds are not enclosed within a fruit.
2. The term "Gymnosperm" means "naked seed" in Greek.
3. They are vascular plants with well-developed xylem and phloem.
4. Common examples include Pine, Cycas, Ginkgo, and Ephedra.
5. Most gymnosperms are woody perennials and include large trees.

2. Characteristics of Gymnosperms

1. Have well-developed roots, stems, and leaves.
2. Vascular tissue is present, but xylem lacks vessels (except in Gnetales).
3. Seeds are exposed on scales of cones (strobili) and are not enclosed in fruits.
4. Pollination occurs mainly by wind (anemophily).
5. Do not produce flowers, unlike angiosperms.
6. Exhibit dominant sporophytic generation and reduced gametophyte.

3. Classification of Gymnosperms

1. Gymnosperms are classified into four major groups:

3.1 Cycadophyta (Cycads)

1. Resemble palms but are gymnosperms.
2. Have unbranched stems and large pinnate leaves.
3. Example: Cycas.

3.2 Ginkgophyta (Ginkgo)

1. Includes a single living species: Ginkgo biloba.
2. Deciduous tree with fan-shaped leaves.
3. Seeds have a fleshy outer layer but are not true fruits.

3.3 Coniferophyta (Conifers)

1. Largest group of gymnosperms.
2. Have needle-like leaves to reduce water loss.
3. Examples: Pinus, Cedrus, Abies.

3.4 Gnetophyta (Gnetales)

1. Have vessel elements in xylem (similar to angiosperms).
2. Some species show double fertilization.
3. Examples: Gnetum, Ephedra.

4. Life Cycle of Gymnosperms

1. Exhibit alternation of generations with a dominant sporophyte phase.

4.1 Sporophyte Stage

1. Diploid and dominant phase.
2. Produces two types of cones:
   • Male cones (Microsporangiate): Produce pollen grains.
   • Female cones (Megasporangiate): Contain ovules that develop into seeds.

4.2 Gametophyte Stage

1. Haploid and reduced.
2. Male gametophyte forms pollen grains, which are carried by wind to female cones.
3. Female gametophyte produces archegonia containing egg cells.
4. After fertilization, the embryo develops inside a seed.

5. Economic Importance of Gymnosperms

5.1 Timber Production

1. Many gymnosperms are used for timber due to their strong wood.
2. Examples: Pine, Cedar, Fir.

5.2 Resin and Turpentine

1. Conifers produce resins used in varnishes, adhesives, and paints.
2. Turpentine oil is obtained from Pinus species.

5.3 Medicinal Uses

1. Ephedra is used to produce ephedrine, a medicine for asthma and cold.
2. Ginkgo biloba is used to improve memory and blood circulation.

5.4 Ornamental and Landscaping

1. Many gymnosperms, like Cycads and Pines, are used for decoration.

5.5 Paper and Pulp Industry

1. Wood from Pines and Spruce is used for making paper.

6. Comparison of Gymnosperms and Angiosperms

7. Conclusion

1. Gymnosperms are ancient seed plants with great economic value.
2. They play a crucial role in timber, medicine, paper, and resin production.
3. Unlike angiosperms, their seeds are exposed and they do not bear flowers.