Heterospory and Origin and Evolution of Seed Habitat in Land Plants – Pteridophytes. Evolutionary Significance of Heterospory and Seed Development in. feature of the seed habit, the enclosure of the female spore; ” Der. Embryosack der s]iorous Pteridophytes there may be little or no difference in the size. Heterospory and seed habit. Reference * Botany for degree students – pteridophyta by:Vasishtha B.R Sinha A.K. Singh V.P *

Author: Sajind Nezil
Country: Guatemala
Language: English (Spanish)
Genre: Photos
Published (Last): 3 November 2011
Pages: 153
PDF File Size: 9.75 Mb
ePub File Size: 6.1 Mb
ISBN: 759-8-99319-348-7
Downloads: 25103
Price: Free* [*Free Regsitration Required]
Uploader: Kesar

Most of the Pteridophytes produce one kind of similar spore. The production of two types of spores with different sexuality was first evolved in Pteridophytes.

Difference between Racemose and Cymose Inflorescence. During this period important heterosporous genera were Lepidocarpon, Lepidostrobus, Mazocarpon, Plaeuromeia, Sigillariostrobiis members of Pteridolhytes Calamocarpon, Calamostachys, Palaeostachys members of Sphenosida. Developments for the availability of sufficient nutrition.

It has been suggested that heterospory arose due to degeneration of some spores in a few sporangia. Give the names few Pteridophtyes which shows heterosporous condition. Range of thallus structure in Algae.

Heterospory and Seed habit in Pteridophytes (Ferns) | Plant Science 4 U

According to Rashid only 9 genera of Pteridophytes are heterosporous. Successful to some extend. The homosporous Pteridophytes show exosporic outside the spore wall gametophytic development.

Stelar Evolution in Pteridophytes. The seed is actually an integumented megasporangium. The gametophytes of the ferns are, however dependent for their nutrition upon soil and environmental condition, whereas in the case of Selaginella, as far as the nutrition of gametophytes is concerned they derive it from the sporophyte, and there they are more independent to the external condition than those of fems.


The next big step in evolution was heterospory or formation of two different types of spores, the smaller ones called microspores and the larger ones known as megaspores.

Differentiate Megaspores and Microscpores. As more nutrition becomes available to less number of spores, the surviving spore grow better, hence increase in their size.

The two types of spores are microspores and megaspores. In this post we will discuss what all stages Pteridophytes successfully completed in forming a seed?

Thus, the heterosporous condition is pterridophytes as precondition for the seed habitat. In heterosporous Pteridophytes the development of micro and megasporangia follow the same pattern. What is the evolutionary significance of Heterospory? One of the most important pteridophyhes of heterospory is the formation of seed habitat.

The condition of the production of two kinds of dissimilar spores, differing in shape and size in the same species, is termed Heterospory. A seed is that ovule which contains an embryo developed as a result of fertilization. In order to overcome this problem, the female gametophyte is permanently retained in the megasporangium. Heterospkry is protected by its wall also but not by an integument. Difference between Microspores and Megaspores. Rounded red circles indicates different steps.

Importance of Heterospory and Seed Habit of Ferns (581 Words)

In heterosporous plants, the male and female gametangia are separated both in time and space. Modification of distal end of megasporangium for pollen capture. They are male spores which on germination produce male gametophyte.


Development of protective layers and nutritive pteridopphytes around megasporangium hetersopory some extend: However, there are some Pteridophytes which produce two different types of spores differing in size, structure and function. In Pteridophytesthese two spores are called as Microspores and Megaspores. These two types of spore differ in their formation, structure and most importantly its functions and sexuality. The condition of Heterospory in Selaginella constitute one of the most important phases in the evolution of the plants.

Advantages and Disadvantages of Vegetative Propagation.

Heterospory and Seed Habit in Pteridophytes | Botany

You may also like…. Heterospory is the production of two or more types of spores. Gametophytic tissue represented by the female gametophyte. Even though, the condition of heterospory is now represented only by eight living species of Pteridophytes, they are Selaginella, Isoetus, Marsilea, Salvinia, Azolla, Pilularia, Regnellidium and Platyzoma.

Heterospory and Seed Habit in Pteridophytes | Botany

The microsporangia contain microspores whereas megasporangia contain megaspores in them. Land plants up to pteridophytes are homosporous. In certain spaces of Selaginella only one megaspore develops within the megasporangium.

There is no embryo sac formation.