If a male angiosperm plant is diploid and its female plant tetraploid, the ploidy level of endosperm will be
Pentaploid
If the female plant is tetraploid, then the central cell of embryo sac, which is a fused polar nuclei, will also be tetraploid. Fusion of the tetraploid central cell to the haploid male gamete forms a pentaploid endosperm.