Within an ovule contained within an ovary of a flower
Explanation;
Angiosperms are the flowering plants. Megasporangia also called female sporangia produce megasporocytes that yield megaspores.
The megaspores develop in the megasporangium and develop into the female gametophyte generation.
The ovule appears to be a megasporangium with integuments surrounding it. Ovules are initially composed of diploid maternal tissue, which includes a megasporocyte. Megaspores remain inside the ovule and divide by mitosis to produce the haploid female gametophyte.