gametofyte

A gametophyte is the haploid multicellular stage in the life cycle of plants and some algae. It arises from a spore and, by mitosis, produces gametes—sperm and eggs—within reproductive structures called gametangia or directly in the tissue. When two gametes unite during fertilization, a diploid zygote forms and develops into the sporophyte, the other major generation in the alternation of generations.

In bryophytes (mosses, liverworts, hornworts), the gametophyte is the dominant, visibly green and photosynthetic generation, while the sporophyte is typically smaller and dependent on the gametophyte for nutrition. By contrast, in vascular plants such as ferns, gymnosperms, and angiosperms, the sporophyte is usually the conspicuous, dominant life stage, and the gametophyte is often reduced and dependent on the sporophyte for resources.

In seed plants, the gametophytes are highly reduced and develop within the tissues of the sporophyte. The male gametophyte is the pollen grain, which delivers sperm to the female gametophyte, while the female gametophyte (inside the ovule) develops into the embryo sac that contains the egg cell. Fertilization results in a zygote that grows into the new sporophyte generation.

Gametophyte morphology and life history vary across plant groups: moss gametophytes are typically larger and independent, fern gametophytes are small and free-living, and seed plant gametophytes are microscopic or highly dependent on the sporophyte. The gametophyte thus plays a central role in sexual reproduction and genetic variation within plant life cycles.