The condition of production of two different types of spores in the same species is known as the heterospory. The spores are differentiated into microspores and megaspores borne on the microsporangium and megasporangium. The microspores develop into male gametophyte whereas the megaspores give rise to female gametophyte. They are also known as the microgametophyte and megagametophyte. The heterospory is noticed in seven genera such as Selaginella, Isoetes, Marsilea, Salvinia, Azolla, Renellidium and Pilularia. The heterospory results in the formation of seed habit. The megaspore containing the female gametophyte derives food from the sporophyte. As it remains inside the sporophyte it is independent of external conditions. It creates a proper nutritive environment for the developing embryo. The integument which protects the ovule and it later transforms to seed coat.
