seeded vascular plants like Gymnosperms became heterosporous, producing two kinds of spores: Megasporangia on modified leaves called megasporophylls produce megaspores that give rise to female gametophytes, and microsporangia on modified leaves called microsporophylls produce microspores that give rise to male gametophytes. Each megasporangium has one megaspore, whereas each microsporangium has many microspores.

Although a few species of seedless plants are heterosporous, seed plants are unique in retaining the megasporangium within the parent sporophyte. A layer of sporophyte tissue called integument envelops and protects the megasporangium.
The whole structure—megasporangium, megaspore, and their integument(s)—is called an ovule.
A microspore develops into a pollen grain that consists of a male gametophyte enclosed within the pollen wall.

The transfer of pollen to the part of a seed plant that contains the ovules is called pollination.
seed plant evolution has included three key reproductive adaptations: the miniaturization of their gametophytes; the advent of the seed as a resistant, dispersible stage in the life cycle; and the appearance of pollen as an airborne agent that brings gametes together.
#gymnosperms

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