Look, endosperm generally formed from fusion of diploid (2n) secondary nucleus in female gametophyte and haploid (n) male gamete..In diploid angiospermic plants. That`s suggest that endosperm possess full ploidy as that of female plant and half ploidy of that male Plant. Hence if female plant is hexaploid then, and male plant is tetraploid, then endoperm will be (6n)(full ploidy )from female +(2n)(half ploid) from male = (8n) means answer is that endoserm is octaploid.
