Heterospory is the occurrence of two kinds of spores, i.e., smaller microspores (producing male gametophyte) and larger megaspores (producing female gametophyte) in the same plant.
Heterospory arose in pteridophytes first. It is common in eight genera of pteridophytes which are Selaginella, Isoetes, Stylites, Marsilea, Pilularia, Regnellidium, Salvinia and Azolla.