According to the five-kingdom classification, given by R.H. Whittaker (1969), the five kingdoms are Monera,
Protista, Fungi, Plantae and Animalia. All the multicellular eukaryotic plants are placed in Kingdom-Plantae. They are autotrophic i.e. they manufacture their food by photosynthesis. In this article, we will focus on one of the important plant groups- Gymnosperms. Furthermore, we will see what are they and focus on the characteristic features and classification of gymnosperms.
What are Gymnospersms ?
“Gymnosperms are plants in which the ovules are not covered by any ovary wall and they remain uncovered, both before and after fertilization.“
Let us break the word into two halves, that is, gymno and sperm. Now, gymnos means naked, whereas, sperma means seed. As a result, plants having naked (gymno) seeds (sperm) are known as gymnosperms.
Furthermore, Gymnospermology is the study of gymnosperms.
The term “gymnosperm” was first used by Theophrastus, in his book Historia Plantarum and Enquiry into Plants.
Further analysis was done by Robert Brown in 1827. He was the one to recognize that gymnosperms as a group distinct from Angiosperms due to the presence of naked ovules.
Gymnospernms Examples :
The gymnosperms include conifers (pines, cypresses, etc.), cycads, gnetophytes, Ginkgo, etc. Some of the pictures of gymnosperms are as follows:
Characteristics of Gymnosperms
The gymnosperms have some characteristic features, such as:
- The main plant body of gymnosperms consists of root, stem and leaves.
- The stems are unbranched (Cycas) or branched (Pinus, Cedrus).
- The leaves can be simple or compound. Also, the leaves in gymnosperms can survive in severe conditions like temperature, humidity and wind.
- Gymnosperms are naked-seeded plants, thus, no fruit formation takes place in these plants.
- They are vascular plants. Therefore, vascular tissues i.e. xylem & phloem are present.
- They are heterosporous plants. They produce two kinds of haploid spores; microspores and megaspores within microsporangium and megasporangium respectively.
- Gymnosperms do not bear flowers.
- Most of the gymnosperms are unisexual, as a result, the chances of self-pollination are low.
- Their growth is slow and they lack vegetative means of reproduction such as by cutting or layering.
- The means of dispersal of seeds are wind, animals or by human beings.
- Gymnosperms are mostly terrestrial and unable to grow in aquatic habitats, except a few.
- Furthermore, roots in some genera have a fungal association in the form of mycorrhiza (Pinus). Whereas, in some others (Cycas) there is an association with Nitrogen-fixing cyanobacteria to form small specialized roots called coralloid roots.
Classification of Gymnosperms
Gymnosperms include both fossils and living forms. They contain primitive members of the Spermatophyta i.e. seed-bearing plants. They form a link between pteridophytes and angiosperms.
Due to extensive records of fossil forms, their classification was difficult. However, they are classified into two groups:
(A) Cycadophyta which consists of:
(1) Cycadofillicales or Pteridospermae (2) Benettitales (3) Cycadales
(B) Coniferophyta which further consists of:
(1) Ginkgoales (2) Corditales (3) Coniferales (4) Gnetales
Let us now discuss these in detail.
The plants in this group consist of the following orders:
- Cycadofillicales or Pteridospermae: This order is extinct. Plant of this order are called seed fern, because of fern-like leaves.
- Benettitales: It is also an extinct order. For example, Williamsonia, which is a fossil plant.
- Cycadales: It includes presently living cycadophytes. Thus, all the plants of this group are living fossils. The plants look palm-like. Male gametes motile. For Example,
- Zamia pygmea, which are the smallest gymnosperm.
- Cycas, also called fern palm or sago palm. Its ovule, male gametes, eggs and male cones are largest in plant kingdom. Furthermore, Cycas lack female cones.
This group is further divided into:
- Ginkgoales: It is the oldest order of coniferophyta. Thus, most of the plants in this order are extinct. These are medium-sized trees. Their leaves are flat and lobed. Male and female flowers form strobili. For example,
- Ginkgo biloba – also known as Maiden hair tree. They are living fossil.
- Corditales: It is an extinct group. It contains large trees with flat, strap-shaped leaves.
- Coniferales: The members of this order are large trees or shrubs. Their leaves are needle or scale-like. The male flowers are arranged in catkins and female flowers in coneIt. It is the largest order in gymnosperm. For example,
- Pinus, Cedrus, Taxus, Sequoia, Araucaria, Metasequoia
- Gnetales: These are small trees, shrubs or climbing shrubs. They have opposite leaves, dicotyledonous embryos and compound cones. It includes most advanced gymnosperms. Plants of this order lack archaeogonia. For example,
- Gnetum, Welwitschia, Ephedra
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