Gymnosperms- Meaning, Definition, Example For All.

                                                  GYMNOSPERMS

Evolution:-

Gymnosperms were the first plants to evolve on earth. The earliest seed-like bodies were found in rocks of the upper Devonian series (about 382.7 million years to 358.9 million years ago). First, all seed plants were Heterosporus meaning two kinds of spores (microspores and megaspores) produced by sporophytes.  Fossil ovules discovered in Scotland suggest that integuments originated during the Mississippian subdivision of the Carboniferous period  (about 358.9 million to 323.2 million years ago). The ovules of Genomosperma kidstonii, for example, consisted of an elongated megasporangium with one functional megaspore and featured eight elongated fingerlike processes that loosely surrounded the megasporangium. In a related species, G. latent, those eight fingerlike processes were fused at the base into a cup and covered the megasporangium rather closely. 

                                                            

The fossil plant Elkinsia polymorpha, a “seed fern” from the Devonian period (about 400 million years ago) is considered the earliest seed plant known to date. Seed ferns produced their seeds along their branches without specialized structures . Gymnosperms expanded in the Mesozoic era (about 240 million years ago), supplanting ferns in the landscape, and reaching their greatest diversity during this time. It has been suggested that during the mid-Mesozoic era, pollination of some extinct groups of gymnosperms was performed by extinct species of scorpionflies that had a specialized proboscis for feeding on pollination drops. The scorpionflies probably engaged in pollination mutualisms with gymnosperms, long before the similar and independent coevolution of nectar-feeding insects on angiosperms. The sperm of modern gymnosperms lack flagella, but in cycads and the Gingko, the sperm still possess flagella that allow them to swim down the pollen tube to the female gamete; however, they are enclosed in a pollen grain.

The Evolution of Sexual Fluids in Gymnosperms:-

Modern Gymnosperms

Pollination drops are widespread among modern gymnosperms, archegonial chamber fluids less so. Pollination drops are produced by the ovule’s diploid nucellus, whereas archegonial fertilization fluids are produced by the ovule’s haploid gametophytes. We will discuss archegonial chamber fluids first. Although their role in sexual reproduction is clear, details of their composition are the most poorly understood of all of the gymnosperm sexual fluids.

Archegonial Chamber Fluid – Function and Composition

This fluid is mainly restricted to cycads and Ginkgo, the extant zooidogamous gymnosperms. Since the process of secretion takes place inside the ovule it is difficult to observe. Accounts of events are mostly of a descriptive, rather than experimental nature. There are conflicting views as to the origins of the fluid(s). Three origins have been proposed. The first of these is the pollen tube. In Dioon edule, as pollen tubes rupture during sperm release, they release a fluid that is of sufficient volume to provide a thin film in which the sperm are able to swim.

A second source is a megagametophyte. In Cycas revoluta, fluids are released from megagametophyte cells lining the archegonial chamber. Cells at the rim of the depression secrete first, followed by cells at the base.

The third source of fluid is from individual archegonia. In Ginkgo biloba, archegonial neck cells release fluid. Combinations of fluids are also possible, e.g., archegonial and pollen tube fluids.

  FIGURE 3

Figure 3. Schematic of ovule tip at time of fertilization, showing layers of integument (I), nucellus (N), megagametophyte (M), with two archegonia (in white), of which one is fertilized (f), the other unfertilized (u). Pollen tubes (p) have grown into the nucellus; the sulcus end of the tube hangs over the archegonial chamber (ac). The archegonial chamber may be filled with fluid (blue) that originates either from ruptured pollen tubes (asterisk), from cells of the megagametophyte that line the chamber, and/or from archegonia. Some published accounts state that fluids from megagametophytes may be sufficient to fill the chamber (blue), or maybe much less abundant, having only the fluids of a few ruptured pollen tubes mixed with secretions from archegonia. In the plant, the orientation of the ovule is reversed, with the megagametophyte at the top.

Conclusion

The two general types of sexual fluids in gymnosperms are pollination drops and fertilization fluids during fertilization. Both occur in ovules. The fertilization fluid originates from gametophytic tissues. We know less about these particular fluids in modern seed plants because we still await chemical analysis of their composition. We know much more about pollination drops. The plesiomorphic pollination syndrome of modern gymnosperms may share features with those of the earliest gymnosperms (i.e., PCM α). Pollination drops represent a significant investment in a fluid by the sporophytic tissues of the ovule. Drops have numerous functions in relatively complex PCMs: they ensure pollen capture, transport, germination and selection, ovule defense, and in some species, nectar reward for pollinators. The ability to present the drop as nectar is found in three of the four major extant clades of gymnosperms, including the two most ancient ones (Ginkgoales, Cycadales). Nectar production may well have also been present in the distant past. We are beginning to understand elements of drop physiology, such as secretion and retraction. As we increase our knowledge of the regulation of secretion we will also begin to broaden our appreciation of nectar secretion by ovules as a unique and important contribution of gymnosperms to the evolution of seed plants.

Meaning of gymnosperms:-

The Gymnosperms (gymnos: naked, Sperma: seeds) are the plants that are not enclosed by an ovary wall and remain exposed.

Definition:-

Gymnosperms are the plants whose ovules are not enclosed by any ovary wall and remain exposed before and after fertilization and are now considered polyphyletic in origin and divided into several extinct divisions. Gymnosperms include medium-sized trees to tall trees and shrubs. 

                                   

What are gymnosperms?

Gymnosperms are the plants whose ovules are not enclosed by any ovary wall and remain exposed before and after fertilization and are now considered polyphyletic in origin and divided into several extinct divisions. Gymnosperms include medium-sized trees to tall trees and shrubs. One of the gymnosperms, the giant redwood tree Sequoia is one of the tallest tree species. The roots are generally tapping roots. Roots in some genera have a fungal association in the form of mycorrhiza (pinus), while in some other (Cycas) small specialized roots called coralloid roots are associated with N2- fixing cyanobacteria. The stems are unbranched (Cycus) or branched (pinus, Cedrus). The leaves may be simple or compound. In cycus the pinnate leaves persist for a few years. The leaves in gymnosperms are well developed to withstand extremes of temperature, humidity, and wind. In conifers, the needle-like leaves reduce the surface area. Their thick cuticle and sunken stomata also help to reduce water loss. The gymnosperms are heterosporous; they produce haploid megaspores and microspores. Two kinds of spored produced within sporangia that are born on sporophylls which are arranged spirally along with the axis form lax to compact strobila or cones. The strobili bearing microsporophylls and microsporangia are called microsporangia or male strobili. The microspores develop into a male gametophytic generation which is highly reduced and is confined to only a limited no. of cells. This reduced gametophyte is called a pollen grain. The development of pollen grains takes place in microsporangia. The cones bearing microsporophylls with ovules or megasporangia are called microsporangia or female strobili. The male-female cones are borne on the same tree (Pinus). However, in cycus male cones are borne on different trees. The megaspore mother cell is differentiated from one of the cells of the nucellus. The nucellus is protected by envelopes and the composite structure is called an OVULE. The ovules are borne on microsporophylls which may be clustered to form female cones. The megaspore mother cell divides itself meiotically to form four megaspores. One of the MEGASPORANGIUM develops into a multicellular female gametophyte that bears two or more ARCHEGONIA or female sex organs. The multicellular female gametophyte is also retained within the megasporangium.

The male and female gametophyte is within the sporangia retained on the sporophytes. The pollen grains are released from the microsporangium. They are carried in air currents and comes in contact with the opening of ovules borne on microsporophylls. The pollen tube carrying male gamete grows towards ARCHEGONIA in the ovules and discharge their contents near the mouth of archegonia. Following fertilization, the zygote develops into an embryo and the ovules into seeds. These seeds are not covered!

                                      

                                                          

Why have gymnosperms remained in so small numbers? 

Gymnosperms have remained in so small numbers because they do not have fruity covering around their seeds so that's why animals didn't show any interest in them and didn't help them to disperse their seeds. That's why they are found in such small numbers.

What are the examples of gymnosperms:-

Conifers

Conifers, in the division Pinophyta or Coniferophyta, are the most numerous of the gymnosperms; woody and with vascular tissue, these are cone-bearing trees and shrubs.

Conifers can be found growing in all parts of the world, although they most notably dominate the boreal forests of the northern hemisphere. Many are adapted to cold climatic conditions, with downward-facing branches, which help to shed snow, and specific biochemical properties that provide resistance to freezing.

Examples of conifers include pines, yews, redwoods, spruces, firs, and cedars.

The conifer forests of the world cover huge areas of land and provide the largest terrestrial carbon sink. Conifers are also valued economically; their softwood is used for the production of paper and timber, they are used to cultivate pine nuts, and the berries of the juniper bush are used to flavor gin.

Cycads

The appearance of the cycads (division Cycadophyta) typically constitutes a single, stout, cylindrical, woody trunk and a crown of large, hard and stiff, evergreen compound leaves, which grow directly from the trunk in a rosette formation. The cycads are dioecious, meaning that each individual plant is either all male or all female.

The cycads are partly xerophyte, which means they are adapted to survive in areas with very little liquid water, although their distribution largely centers around the subtropical Tropic of Cancer and the Tropic of Capricorn, as well as tropical regions such as Central and South America, China and South East Asia, India and Sri Lanka, Madagascar, and Tropical and Southern Africa.

The cycads were much more numerous in the past than today, peaking in ‘the age of the cycads’ – the Jurassic period. There are only three extant families within the cycads today: the Cycadaceae, Stangeriaceae, and Zamiaceae.

Gnetophytes

The Gnetophyta are distinguishable within the gymnosperms because they have vessel elements, a system of channels mostly found in the angiosperms, which transport water within the plant.

Covering 70 species over three genera, the Gnetophyta are morphologically variable, including trees, shrubs, stumps, vines, and creepers with leaf shapes ranging from opposite to whorled, scale-like, and straplike.

The distribution is determined by the genus: Welwitschia is unique to the Namib Desert and surrounding areas in South West Africa; Gnetum are found in tropical forests; and Ephedra are found mostly in arid or desert areas of southwest America, North Africa, Southern Europe, and Central Asia.

Ginkgo

The closest relatives to the cycads, Gingko is a genus of gymnosperm of which Gingko Biloba is the sole extant species.

Ginkgos are large, slender, shade-intolerant trees, growing up to 160ft with distinctive fan-shaped leaves. They are deep-rooted and resistant to damage from wind and snow. They are also resistant to disease and insect damage, owing to an exceptionally large genome, which enables antibacterial and chemical defense mechanisms.

Gingko first appears within the fossil record in the Permian period, 270 million years ago, and the Gingko Biloba remains largely unchanged today, earning it a classification as a ‘living fossil’.

Native only to China, Ginkgo biloba is cultivated globally for use in various traditional medicines and as a food source. 

           

What is the difference between gymnosperms and angiosperms?

Here is the difference given:-

Parameter	Angiosperms	Gymnosperms
Definition	These are seed-producing flowering plants whose seeds are enclosed within an ovary.	These are seed-producing non-flowering plants whose seeds are unenclosed.
Seeds	Their seeds are enclosed inside an ovary, usually in a fruit.	Their seeds are bare and not enclosed, which are found on scales, leaves, or as cones.
Life Cycle	The lifecycle of these plants is seasonal because these die during autumn/fall.	These plants are evergreen in nature.
Presence	These are present in flowers and can be unisexual or bisexual.	These are present as cones and are unisexual.
Reproduction	Reproduction is depending on the animals for spread.	Here, Reproduction is depending on wind for spread.
Tissue	These have triploid tissue.	These have haploid tissue.
Leaves	The shape of the leaves is flat.	Their leaves are scale-like and needle-like.
Wood	These have hardwood.	These have softwood.
Uses	Used for Medications, food, clothing, etc.	Used for Paper, Lumber, etc.

Some facts:

1. Reproduction:

Reproduction in the angiosperms can be unisexual or bisexual. The gametes are being spread by wind and by the insect as well as by animal pollinators, attracted by their flowers. Their flowers are having both female and male gametes inside themselves. Also, after fertilization, the ovules develop into a fruit.

The gametes of the gymnosperms are found in cones. Fertilization is described as single. Thus the pollen grains fall and germinate directly on the ovules. Pollen spores are spread by wind alone.

2. Uses:

Angiosperms are providing virtually all plant-based food as well as the most livestock feed. Grains, fruit, legumes, nightshades which include potatoes and tomatoes, gourds, and cabbages are all angiosperms. Other angiosperms are like cotton and flax provides paper and textiles. The hardwood of angiosperms is useful to make the hardwood floors.

Gymnosperms are from the conifer group like pine, spruce, and fir and are commonly in use for lumber. Other gymnosperms are processed into other products such as soap, varnish, and perfumes.

What are the uses of gymnosperms? 

1. Gymnosperms are a good source of food. Seeds of these non-flowering plants are widely used as an edible species, used for producing various food products. These plant species include Ginko, pinus, cycas, etc.
2. A few species of gymnosperms are a good source of starch and are also used in the production of sago. It serves as a major staple food for lowland or indigenous peoples.
3. In certain parts of America and in other lowland regions, the leaves of these plant species are soaked and eaten as green leafy vegetables.
4. The different species of non-flowering plants are widely used in the production of wine and also on other food products.
5. Other than the food, gymnosperms are widely used by the pharmaceutical industry for the production of various medicines, which are effectively used to treat infectious diseases and other allergies including cold, cough, asthma, bronchitis, etc.
6. Taxus, a genus of coniferous trees is well known for the drug taxol. This is an anticancer drug, which is used in the treatment of different cancers and is prepared from the bark of the Taxus tree.
7. Different species of Cycas plants are used in the treatment of different diseases and also in the production of different hair care products, including oil, lotion, shampoo, etc.
8. There are a few species of non-flowering plants, which are widely used as ornaments for decoration purposes. For example- fern.
9. Oil extracted from the barks, wood, and other parts of the plants is used in the cosmetics industries in the production of perfumes, room fresheners, and other fragrance spray.
10. Other than the food and medical applications, a few of these non-flowering plants are widely grown in gardens, parks, and other places as these plants possess beautiful ornamental leaves.

Other than these significances, gymnosperms have further economical importance too. These species are widely used in the production of:

1. Certain medicines for the treatment of malignant ulcers.
2. Mounting medium during microscopic examination in laboratories.
3. A gum extracted from cycas trees is used as the antidote for snake bites.
4. The wood of these plants is widely used in paper manufacturing industries.
5. The leaves of cycads are used for preparing handbaskets, brooms, hats, door and floor mats, and other eco-friendly products.
6. Similar to teak and rosewood, the wood obtained from the barks, stem, and the branches of the pines trees are also used for the production of beams, doors, flooring, poles, railway wagon, etc.

  

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