gametophytes

Gametophyte refers to the haploid phase of the plant life cycle in alternation of generations. It develops from a spore by mitosis and produces haploid gametes (eggs and sperm) by mitosis as well. Fertilization between compatible gametes restores the diploid condition and gives rise to the sporophyte, the next generation.

In many land plants, the gametophyte is free-living and photosynthetic, notably in bryophytes (mosses, liverworts, hornworts) and many ferns. The sporophyte, by contrast, is often attached to or dependent on the gametophyte for nutrition and support, especially in bryophytes.

In seed plants, the gametophytes are highly reduced and dependent on the sporophyte. The male gametophyte appears as pollen grains produced in the anthers; the female gametophyte develops within the ovule and is typically microscopic. Pollen delivers sperm to the ovule, enabling fertilization and the formation of a zygote.

Gamete-producing organs include archegonia (egg-producing) and antheridia (sperm-producing) in many non-seed plants. In seed plants, the fertilization process is aided by pollen tubes that transport sperm to the egg.

Gametophyte life stages show variation across groups: some lineages have isomorphic gametophytes, while others exhibit reduced or highly specialized forms. The transition between dominant gametophyte and dominant sporophyte life cycles reflects major evolutionary shifts in land plant history.