Short answers, pulled from the story.
A gametophyte is the haploid multicellular phase in the life cycles of plants and algae, carrying one set of chromosomes. It is the sexual phase, developing sex organs that produce gametes which join in fertilization to form a diploid zygote.
The gametophyte is haploid with one set of chromosomes and produces gametes, while the sporophyte is diploid with a double set of chromosomes and produces haploid spores by meiosis. The two phases alternate, each generation building the other.
In bryophytes, which include mosses, liverworts, and hornworts, the gametophyte is the most visible stage because it is longer lived and nutritionally independent. The sporophytes stay attached to the gametophytes and depend on them.
In most ferns, such as the leptosporangiate fern Dryopteris, the gametophyte is a free-living photosynthetic organism called a prothallus. In the clade including Ophioglossaceae and Psilotaceae, the gametophytes are instead subterranean and survive through mycotrophic relationships with fungi.
The cell number varies by order, with Cycadophyta having 3 celled pollen grains and Ginkgophyta having 4 celled grains. Gnetophyta have 2 or 3 cells depending on species, while Coniferophyta range widely from single celled to 40 celled.
A typical angiosperm female gametophyte, or embryo sac, contains 7 cells with 8 nuclei, made up of 1 egg cell, 3 antipodal cells, 2 synergid cells, and a central cell with two nuclei. Special cases range from 4 cells with 4 nuclei to 10 cells with 16 nuclei.
No extant gametophytes have stomata, but they have been found on fossil species such as the early Devonian Aglaophyton from the Rhynie chert. Other Rhynie chert fossil gametophytes were far more developed than present forms, with a conducting strand, cortex, epidermis, and a cuticle with stomata.