Gymnosperms
Gymnosperms are seed bearing plants without flower and fruits, represented by about 900 living species all over the world
Characteristics of gymnosperms
- Gymnosperms are regarded as an intermediate group between the pteridophytes and angiosperms. They formed a dominant vegetation on the earth about 200 million years ago and now they have maintained their dominance in the colder regions. A few are in warmer climate also.
- The plants are with roots, stems and leaves. These plants bears naked seeds. All gymnosperms are perennial woody trees. Some of them are large and live for thousands if years.
- The roots are generally taproot, in some species mycorrhiza, corolloid roots and root with cyanobacteria are seen.
- The stems are branched or unbranched.
- The leaves may be simple or compound. In Cycas leaf is pinnate and persists for a few years and young leaves circinate venation. In Pinus leaves are needle like to reduce the surface area. Thick cuticle and sunken stomata in gymnosperms help to reduce the water loss.
- Vascular tissues in roots, stems and leaves are xylem and phloem arranged into vascular bundles. Xylem has tracheid's, xylem parenchyma and xylem fibers. Phloem is without companion cells, instead they have albuminous cells.
- Gymnosperms are heterosporous, i.e. produce two types of spores- microspores and megaspores.
- Sexual reproduction does not require water as pollen grains are carried by wind. Meiosis in microsporangia and megasporangia results in the formation of haploid microspores and megaspores.