Short answers, pulled from the story.
The gametophyte is a haploid multicellular organism that carries only one set of chromosomes. It serves as the sexual phase in the life cycle of plants and algae by developing sex organs to produce gametes.
Ulva lactuca exhibits an isomorphic relationship where sporophytes and gametophytes appear externally identical to the human eye. In this species, all gametes are isogamous, meaning they share the same size, shape, and morphology without visual differences between male and female forms.
Mosses, liverworts, and hornworts feature a gametophyte that is the most visible and nutritionally independent stage of their life cycle. Ralf Reski published research in 1998 detailing the development and genetics of these mosses while noting that sporophytes attach to and depend entirely on them for survival.
Homosporous vascular plants like clubmosses and many ferns produce only one type of spore leading to bisexual or monoicous gametophytes. Heterosporous vascular plants such as Dryopteris develop endosporically within the spore wall to create distinct microgametophytes and megagametophytes that are either dioicous or monoicous.
Cycadophyta orders produce three-celled pollen grains while Ginkgophyta species create four-celled versions with mobile germ cells containing flagella. Coniferophyta pollen grains range from single celled to forty celled depending on the species, where some cells function as tube cells and others serve vegetative roles.
Tilia americana flowers display typical seven-celled eight-nucleate female gametophytes known as embryo sacs. Development via mitosis results in specific roles including one egg cell, three antipodal cells, two synergid cells, and a central cell holding two nuclei before double fertilization occurs.