The heterosporous pteridophytes show certain characteristics, which are precursor to the seed habit in gymnosperms. Explain.

The plants which produce two types of spores with different sizes, large →macro) and small →micro), are called heterosporous. It is found in genera like Salvina and Selaginella. The megaspores produce megagametophytes →female gametophytes) and microspores produce microgametophytes →male gametophytes). The female gametophytes in these plants are retained on the parent sporophytes for variable periods. The development of the zygotes into young embryos takes place within the female gametophytes. The presence of heterospory in pteridophytes indicates the evolution of gymnosperms from pteridophytes.