are heterosporous
This is the production of spores by plants that are in various sizes and sexes. The smaller spore is the male known as microspore and the large one is the female or the megaspores. Heterospory evolved during a period from isospory independently in some plants such as the clubmosses, arborescent horsetails and some gymnosperms. This occured as a process of the evolution in the time of the sex differentiation in plants.