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A sporophyte is the structure of a plant or alga that has a diploid set of chromosomes. It is seen in all plants and in some algae. The sporophyte produces spores (hence the name), by meiosis. These spores develop into a gametophyte. Both the spores and the resulting gametophyte are haploid, meaning they only have one set of homologous chromosomes. The gametophyte produces male or female gametes (or both) by mitosis. The fusion of male and female gametes produces a zygote which develops into a new sporophyte. This cycle is known as alternation of generations. In the normal course of events, the zygote and sporophyte will have a full set of chromosomes again. An exception is when a diploid and haploid gamete fuse, resulting in a triploid sporophyte, which will usually be sterile, as dividing three sets of chromosomes into two halves causes complications. The sporophyte is the dominant form in algae, ferns, gymnosperms, and angiosperms (flowering plants). Bryophytes (mosses, liverworts and hornworts) have a dominant gametophyte stage.
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