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In botany , in contrast to isospore, heterospore is understood to mean the phenomenon that the spores of a species have different sizes and look different. The male gametophyte develops within the smaller microspores and the female gametophyte develops in the larger megaspores (macrospores). The gametophytes ( prothallia ) are also of different sizes and develop within the spore wall. This phenomenon is called endospore .

The heterosporia is a characteristic of the moss ferns ( Selaginella ), the bream herbs (Isoetales), the water ferns ( Salvinia , Azolla , Pilularia and Marsilea ) and the seed plants .