Heterospory evolved during the Devonian period from isospory independently in several plant groups: the clubmosses, the arborescent horsetails, and progymnosperms. This occurred as part of the process of evolution of the timing of sex differentiation.

How did heterospory evolve?

The evolution of bimodal size distributions with small male spores and large female spores, known as heterospory, was an innovation that occurred repeatedly in the history of land plants. ... With the advent of such microspores, megaspores would evolve under frequency-dependent selection.

Why is heterospory of evolutionary significance?

- Heterospory is thus considered an important step in evolution as it is a precursor to the seed habit. - Heterospory evolved first in pteridophytes such as Selaginella and Salvinia. - The seed habit is the most complex and evolutionary successful method of sexual reproduction.