Endosperm are

Endosperm is Triploid.
The endosperm is a tissue produced inside the seeds of most flowering plants following double fertilization.
Endosperm is formed when the two sperm nuclei inside a pollen grain reach the interior of a female gametophyte. One sperm nucleus fertilizes the egg cell, forming a zygote, while the other sperm nucleus usually fuses with the binucleate central cell, forming a primary endosperm cell. That cell created in the process of double fertilization develops into the endosperm.