What important evolutionary step is indicated by the development of zygotes within the female gametophytes?

Step-by-step solution

Zygote thereafter produces a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes. In the majority of the pteridophytes all the spores are of similar kinds; such plants are called homosporous. Genera like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores, are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. The female gametophytes in these plants are