Endosperm in the seed of gymnosperms and most flowering plants, a tissue in which the nutrient substances necessary for the development of the embryo are deposited. In gymnosperms the endosperm is formed in the ovule during germination of the megaspore; it consequently becomes the female prothallus (gametophyte), with a haploid set of chromosomes. The archegonia in gynosperms develop from certain cells of the endosperm.
The ploidy level of endosperm of gymnosperm is haploid i.e 1n.
The endosperm in gymnosperms is haploid because it is formed from the haploid megaspore by repeated divisions. This endosperm consequently develops into female gametophyte with haploid chromosomes.