bio

Heterospory

Producing two kinds of spore instead of one: small spores that grow into male gametophytes, large spores that grow into female ones. It sounds like a minor taxonomic detail and is in fact the architectural precondition for the seed. Once the female spore is large, few in number and retained inside the parent body — and once the gametophyte develops entirely within the spore wall rather than outside it — every component of a seed is present and only needs rearranging.