What is heterospory? Briefly comment on its significance. Give two examples.

(N/A) Heterospory is a phenomenon in which two kinds of spores are produced by the same plant. These spores differ in size: the smaller one is known as the $microspore$ and the larger one is known as the $megaspore$.
The $microspore$ germinates to form the male gametophyte,while the $megaspore$ germinates to form the female gametophyte. The male gametophyte releases male gametes,which reach the female gametophyte to fuse with the egg.
The development of the zygote occurs inside the female gametophyte. This retention and germination of the $megaspore$ within the $megasporangium$ ensures the proper development of the zygote into the future sporophyte.
Heterospory is considered a crucial evolutionary step because it is a precursor to the seed habit. The evolution of the seed habit is directly related to the retention of the $megaspore$.
Examples of plants exhibiting heterospory include $Selaginella$ and $Salvinia$.