Ferns - Polyploidy

In many species of ferns, the sporophyte phase is diploid (two sets of chromosomes) and the gametophyte phase is haploid (one set of chromosomes). However, many other ferns are considered polyploid, in that their sporophyte contains three or more sets of chromosomes. In polyploid ferns, the gametophyte and sporophyte phases are said to have the "reduced" and the "unreduced" number of chromosomes, respectively.

Apospory and apogamy are special types of asexual reproduction which have important roles in the generation and proliferation of polyploidy. In apospory, the gametophyte develops directly from special cells on the sporophyte, so that the gametophyte and sporophyte both have the unreduced number of chromosomes. The sperm and egg cells produced by such a gametophyte have twice the original number of chromosomes. In apogamy, the sporophyte develops directly from special cells on the gametophyte, so that the sporophyte and gametophyte have the same reduced number of chromosomes. Apogamy typically occurs in gametophytes which themselves have arisen by apospory.