gametofyytti

Gametofyytti, the Finnish term, is known in English as the gametophyte. It is the haploid phase of the plant life cycle in alternation of generations. It arises from a spore produced by the diploid sporophyte through meiosis and grows by mitotic division. The gametophyte produces the gametes—sperm and eggs—either directly on its tissues or within specialized organs called antheridia and archegonia. Fertilization of an egg by a sperm forms a diploid zygote that develops into the sporophyte, completing the cycle.

Across plant lineages the prominence of the gametophyte varies. In bryophytes (mosses, liverworts, hornworts) the gametophyte is the dominant, free-living stage, while the sporophyte is typically dependent on it. In ferns and many other pteridophytes the gametophyte is usually small and short-lived, with the sporophyte as the conspicuous phase. In seed plants (gymnosperms and angiosperms) the sporophyte is dominant, and the gametophytes are highly reduced and develop within the sporophyte's tissues: male gametophytes are pollen grains and female gametophytes are the embryo sacs inside ovules.

Because the gametophyte produces gametes by mitotic division, it maintains a haploid genome, while meiosis occurs in the sporophyte to produce spores that seed new gametophytes. The study of gametophytes informs our understanding of plant reproduction, the evolution of alternation of generations, and how plants adapt to diverse habitats.