Fertilization in flowering plants is called double fertilization.

Explanation

i. The pollen tube bursts and releases two male gametes in the embryo sac.
ii. One male gamete fuses with the egg cell to form zygote,whereas the second male gamete fuses with two polar nuclei in the embryo sac to form endosperm.
iii. Since, in flowering plants the process of fertilization occurs twice in the same embryo sac, by two male gametes,it is called as double fertilization.