The endosperm is a storage tissue found in many dicot and all monocot seeds.
It is the result of the fusion between one sperm nucleus and two female polar nuclei during the process of double fertilization.
All dicot seeds have an endosperm that is produced during seed development.
However in some species, the endosperm is used up during development and these dicot seeds store food reserves in their large cotylendons.
In many other dicots, the endosperm persists throughout development and is seen in the mature seed.