The generation in the life cycle of a plant that bears the gamete-producing sex organs. The gametophyte is haploid. It is the dominant phase in the life cycle of mosses and liverworts, the sporophyte generation depending on it either partially or completely. In clubmosses, horsetails, and ferns it is the prothallus. In seed plants it is very much reduced. For example, in angiosperms the pollen grain is the male gametophyte and the embryo sac is the female gametophyte. See also alternation of generations.