gametophyte

The gametophyte is the haploid, multicellular generation in the life cycle of many plants and some algae, arising from a spore by mitotic division. It produces gametes—sperm and eggs—also by mitosis within specialized organs called gametangia. Fusion of two gametes creates a diploid zygote, which grows into the sporophyte, the other generation in the life cycle.

In bryophytes, including mosses, liverworts, and hornworts, the gametophyte is the dominant, conspicuous stage and is typically photosynthetic. The sporophyte is usually diminutive, short-lived, and dependent on the gametophyte for nutrients, often remaining physically attached to it.

In ferns and other pteridophytes, both the gametophyte and the sporophyte can be free-living, though they differ in size and appearance. The gametophyte, often called a prothallus, is usually small and heart-shaped, requires moisture for fertilization, and hosts both archegonia (egg-producing structures) and antheridia (sperm-producing structures). Fertilization produces a zygote that grows into the sporophyte, which becomes the dominant generation.

In seed plants (gymnosperms and angiosperms), the gametophyte is highly reduced and entirely dependent on the sporophyte. The male gametophyte develops into a pollen grain, and the female gametophyte develops within the ovule. Pollen germination and sperm delivery lead to fertilization, producing an embryo that develops into the new sporophyte within a seed.

Overall, the gametophyte completes the haploid phase of the plant life cycle and is central to sexual reproduction and genetic variation.