Evolutionary Significance of Polyploidy in the Pteridophyta

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Abstract
Polyploidy occurs in the heterosporous and homosporous Pteridophyta, but with a much higher frequency in the latter. Ninety-six percent of the homosporous Pteridophyta show a gametic chromosome number greater than 27, whereas 90 percent of the heterosporous ones possess a gametic chromosome number less than 28. Ultrafrequent establishment of polyploidy in the homosporous Pteridophyta appears to be necessary to create and maintain genetic variation in the face of the homozygotizing effects of habitual self-fertilization in the monoecious gametophytes of these plants.