gametofitu

Gametofitu, commonly referred to in English as the gametophyte, is the haploid phase of the life cycle in plants and algae that exhibit alternation of generations. It is a multicellular structure that produces gametes—sperm and eggs—by mitotic division.

The gametophyte develops from a spore that germinates after meiosis in the diploid sporophyte. The sporophyte and gametophyte alternate, each generation giving rise to the other.

Male gametophytes form in antheridia and female gametophytes in archegonia. The sperm produced in antheridia fertilize eggs in archegonia; fertilization results in a diploid zygote that develops into the sporophyte.

For many algae and all land plants, the degree of dominance of the gametophyte varies. In bryophytes (mosses, liverworts, hornworts) the gametophyte is the dominant, photosynthetic, independent generation, while the sporophyte is small and dependent. In ferns and other pteridophytes the sporophyte is the dominant, free-living generation and the gametophyte is typically smaller and short-lived. In seed plants (gymnosperms and angiosperms) the gametophyte is highly reduced and dependent on the sporophyte: the male gametophyte is the pollen grain, and the female gametophyte is the embryo sac contained within the ovule.

Fertilization in seed plants does not require free water, whereas in many bryophytes and some algae, motile sperm depend on a film of water to reach the egg.