The plant part formed by the successful union of a male pollen cell and a female ovule, carrying characteristics of both parents, is called a zygote.

Here's a breakdown:

* Pollen cell: The male gamete, containing half the genetic information of the male parent.

* Ovule: The female gamete, containing half the genetic information of the female parent.

* Zygote: The fertilized ovule, resulting from the fusion of the pollen cell and ovule. It now contains the complete genetic information from both parents.

The zygote will then develop into a seed, which contains the embryo of the new plant, inheriting traits from both parents.