 Because the Marsileaceae produce two kinds of spore ( and thus two kinds of gametophyte ) , they are called heterosporous . While <unk> is the norm among all plants with seeds , such as the flowering plants and conifers , it is very rare among other groups of plants . Also , most heterosporous plants produce their two kinds of sporangia in different places on the plant . Since the Marsileaceae grow both kinds together in a single cluster , they differ from other plants in this regard as well . 
