Gametophytes of sexually reproducing flowering plants are

In the life cycle of sexually reproducing flowering plants (angiosperms), there is an alternation of generations between a diploid sporophyte and a haploid gametophyte [1]. The gametophyte is the multicellular haploid generation that develops from haploid spores produced through meiosis [2]. In angiosperms, these gametophytes are highly reduced and develop within the specialized organs of the flower [1]. The male gametophyte is the pollen grain (microgametophyte), which develops in the anther, while the female gametophyte is the embryo sac (megagametophyte), which develops within the ovule [2]. Both are haploid structures that produce gametes (sperm and egg cells) via mitosis [3]. Upon fertilization, the fusion of these haploid gametes restores the diploid state, forming a zygote that develops into the next sporophyte generation [3].

Sources

1. [1] https://core.ac.uk/download/pdf/206700467.pdf
2. [2] https://pmc.ncbi.nlm.nih.gov/articles/PMC3268550/
3. [3] https://www.ncbi.nlm.nih.gov/books/NBK9980/