Heterospory and Seed Habitat
(Origin of Seeds and Seed Habitat in Vascular Plants from Heterospory)
Heterospory is the production of two or more types of spores
Heterospory is a condition of the production of more than one type (usually two) of spores in a single plant. These two types of spore differ in their formation, structure and most importantly its functions and sexuality.
In Pteridophytes, these two spores are called as Microspores and Megaspores.
Microspores are small sized spores produced in large numbers inside the microsporangium. They are male spores which on germination produce male gametophyte.
Megaspores are comparatively large spores produced in limited numbers (1 to 4) inside the megasporangium. They are female spores which on germination produce the female gametophyte.
Learn more: Difference between Microspores and Megaspores
The production of two types of spores with different sexuality was first evolved in Pteridophytes. 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.