katteseemnetaimedele omane protsess, mida iseloomustab lisaks spermi ja munaraku ühinemisel toimuvale diploidse kromosoomide arvuga sügoodi tekkele teise spermi ühinemine lootekoti tsentraalraku kahe haploidse tuumaga triploidse endospermi tekkimisega, A complex fertilization mechanism of flowering plants (angiosperms). In addition to the merging of a sperm and egg forming a diploid embryo, a female gametophyte merges with two male gametes, forming a triploid endosperm.