Gametophyte

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In plants that undergo alternation of generations, a gametophyte is the structure, or phase of life, that contains only half of the total complement of chromosomes:

The sporophyte produces spores, in a process called meiosis. These spores develop into a gametophyte. These spores and the resulting gametophyte have only half of the total complement of chromosomes.
The gametophyte produces male or female gametes (or both), in a process called mitosis. The fusion of male and female gametes produces a zygote which develops into the sporophyte.

In mosses (bryophytes) the gametophyte is the commonly known phase of the plant. An early developmental stage in the gametophyte of both mosses and ferns (immediately following the meiospore) is called the Protonema.

In most other plants the gametophyte is very small (as in ferns) or even reduced as in flowering plants (angiosperms), where the female form (ovule) is known as a megagametophyte and the male form (pollen) is called a microgametophyte.