What structure forms during angiosperm fertilization but does not form during fertilization among other types of plants?

The answer is ' triploid cell'.

This occurs when two sperm nuclei reach the interior of a female gametophyte, where one sperm will fertilise the egg cell to form a zygote, whereas the other usually fuses with the binucleate central cell, forming a primary endosperm cell, effectively constituting an organism separate from the growing embryo. Approximately 70% of angiosperm species have polyploid endosperm cells which are typically triploid (containing three sets of chromosomes), but can vary widely from diploid (2n) to 15n.