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What is the role of a fern gametophyte in reproduction?

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tree fern — Fern Tree fern (*Cyathea medullaris*).

The fern gametophyte, often called a prothallium, is a small, typically heart-shaped structure that plays a critical role in the fern life cycle by producing sex cells.12

Developing from a spore, the gametophyte functions as the sexual phase of the plant. Most fern prothalli are bisexual, meaning they develop both male and female sex organs on their undersurface:12

Antheridia: These organs produce sperm, which are equipped with cilia for locomotion.32
Archegonia: These organs house the egg.32

Fertilization requires free water, through which the sperm swim toward the archegonia, guided by organic acids released at the opening. Once an egg is fertilized, the resulting zygote develops into a juvenile sporophyte. During this early stage, the young sporophyte relies on an organ called a foot to absorb nutrients from the gametophyte until it becomes established and the parental gametophyte dies.312