Hello aspirant,

A sporangium that develops only megaspores inside the ovary is known as megasporangium. Megasporangia (female sporangia) produce megasporocytes (megameiocytes) that gives birth to megaspores.

The characteristics of megasporangium is that it plays an important role in sexual reproduction. When a pollen grain lands on the stigma of a flower of its same species, it transmits a pollen tube down along the style. This tube then enters the ovary and gets into the ovule of the plant. When that happens, fertilization can begin as the nucleus of the pollen grain is sent down the tube to fuse with the nucleus in the embryo sac.

Hope this helps,

All the Best!!