Final answer:
Microsporangia, where pollen grain development takes place, are found in the anther of a plant's stamen.
Step-by-step explanation:
The microsporangia are located in the anther of a plant's male reproductive structure. These are the sites where the development of pollen grains occurs. Within each microsporangium, microspore mother cells undergo meiosis to produce microspores, which will ultimately become pollen grains. The anther, supported by the filament part of the stamen, provides the environment necessary for the maturation of the male gametophytes, or pollen grains.