Examples of Heterosporous Pteridophytes
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Examples & Advantages of Heterospory | Disadvantages of Heterospory

Heterospory

What is Heterospory? 

Heterospory is the development of spores of various sizes and sexes by land plant sporophytes. The smaller microspore is male, while the larger megaspore is female. Several plant groups, including clubmosses, arborescent horsetails, and progymnosperms, independently evolved heterospory from isospory during the Devonian period. This happened as a result of the evolution of the timing of sex differentiation.

Heterospory is a type of spore formation in which the sporogenous cells are not all derived from one parent cell.  It can be found in some plants, such as ferns and mosses.

Heterospory is found in the late flowering plants, where it may be a derived state or ancestral to the current sporophyte generation of angiosperms; in other words, heterospory may be the original condition for flowering plants.

Heterospory is found in a wide range of plants, and the exact definition of what constitutes heterospory has been unclear. It has been defined as the storage of one or more mature pollen mother cells (M) in an ovule, but other features have not been considered. The definition has limited the assessment of heterospory to the ‘stored pollen’ type.

Origin of Heterospory

Based on fossil evidence, heterospory is thought to have evolved during the Devonian period, mostly in wet/damp environments. In addition to being the result of light competition, it is believed that heterospory was more competitive in wetter areas because the megaspore could travel more easily around in an aquatic environment, while microspores were more easily dispersed by wind.

Many fossilized plant species have been found to have spores of varying sizes. For example, the fossilized species Lepidophloios, also known as the scale tree, was heterosporous; the scale tree had separate cones containing either male or female spores on the same plant.

Endospory occurs in modern heterosporous plants such as many ferns. A megagametophyte is fertilized by a microgametophyte while still within the spore wall, receiving nutrients from the inside of the spore.

Endospory and heterospory seem to be two of the several precursors to seed plants and the ovary. Their most successful and widespread descendants are heterosporic plants that grow seeds.  Seed plants are the most numerous type of heterosporic plant.

Heterospory is a type of plant reproduction where pollen goes from the male anther to the female stigma. This process also occurs in gymnosperms and some angiosperm plants. It is a type of sexual reproduction, and fertilization is not carried out in the ovaries.

Heterospory does not happen in all plants. It only happens in those plants that do not produce flowers or do not have pollination from animals. There are many heterosporous plants, such as ferns, cycads, and conifers. Fertilization is not done inside the flower.

Heterospory Examples

Heterospory is a type of spore formation in plants that occurs when the plant’s sporophyte produces two different kinds of spores. The heterosporous condition has been observed in many families of flowering plants, including the grasses and sedges and some conifers.

Examples of heterospory plants are Selaginella, Salvinia, and Marsilea, etc.

Examples of Heterosporous Pteridophytes
Salvinia: Examples of Heterosporous Pteridophytes >Source

Advantages of Heterospory

Heterospory is beneficial since having two distinct forms of spores increases the likelihood of plants successfully producing offspring. Heterosporous spores may react to environmental selection independently in order to improve male and female reproductive function.

Endosporic gametophytes in heterosporous forms are independent of external factors and self-sufficient in the food supply. As a result, the female gametophyte that grew inside the large megaspore at the cost of reserver food is better positioned for embryo initiation. The free-living exosporic gametophytes of homosporous members, on the other hand, are completely dependent on external conditions.

The sizes of their gametophytes are drastically reduced as a result of heterospory. The male gametophyte is drastically reduced, and in most instances, it is nothing more than an antheridium. The female gametophyte never outgrows the megaspore’s limits.

At the spore level, sex differentiation in heterosporous forms can be predicted. As a result, sex differentiation may be extended from the early gametophyte stage to the sporophyte.

Disadvantages of Heterospory

Heterospory is a form of sexual reproduction where the plant produces two different types of gametes. There are many disadvantages to heterospory, including reduced genetic diversity and increased vulnerability to disease.

The disadvantageous effects of heterospory have been documented in plants such as cucumbers, squash, watermelon, tomatoes, and corn.

Another disadvantage of heterospory is that it does not produce as many seeds per plant. Plants with heterospory also have a slower growth rate than those without. Heterospory also limits the diversity of species within an ecosystem.

Another disadvantage of heterospory is the longer time it takes for a plant to mature, sometimes up to 10 times as long. The longer propagation period is problematic for many reasons, not least because the plant could be susceptible to disease and insect damage.

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