(botany) A phase in the life cycle of certain plants and algae that starts with a spore up to the time that gametes are produced
In plants and certain algae (e.g. Archaeplastida and Heterokontophyta), their life cycle is comprised of two phases (or generations): the phase of gametophyte and the phase of sporophyte. This type of life cycle wherein there are two alternating phases is called alternation of generations. In particular, it is the alternation of diploid and haploid forms.
In plants, the gametophyte generation is one that which begins with a spore that is haploid (n). The spore undergoes series of mitotic divisions to give rise to a gametophyte. A gametophyte is a haploid multicellular plant form. It would therefore have only one set of chromosomes. The gametophyte phase is the sexual phase in the life cycle and therefore the plant would develop sex organs that produce gametes, which are also haploid. The gametes that participate in fertilization would later enter the sporophyte generation characterized by the plant form that is diploid following the union of gametes.
In algae with alternation of generations, the sporophyte and the gametophyte are independent organisms. Similar to plants’ gametophyte generation, the algal gametophyte is the sexual phase.