The male sex cell in a plant is called a sperm cell or sperm nucleus. It is produced within the pollen grain, which is the male gametophyte of flowering plants.

Here's a breakdown:

* Pollen Grain: This is the structure that carries the male sex cells. It is produced within the anther of the stamen, a part of the flower.

* Sperm Cell: Inside the pollen grain, the sperm cell develops from a generative cell. When the pollen grain lands on the stigma of a flower, the sperm cell travels through the pollen tube to the ovule, where it fertilizes the egg cell.

Therefore, the sperm cell plays a crucial role in plant reproduction by contributing its genetic material to the formation of a new plant embryo.