(Polypodium appalachianum)
Polypodium appalachianum-is a fern species native to eastern North America. Sometimes called the-Appalachian polypody-or-Appalachian rockcap fern, it is very similar in appearance to-Polypodium virginianum. For years,-P.-virginianum--- long considered a variety of the British-Polypodium vulgare--- was recognized as having cryptic races, with diploid, triploid, and tetraploid representatives. Since the triploid specimens bore abortive spores, it was apparently the hybrid between the diploid and tetraploid groups. In 1991, it was resolved that the type of-P.-virginianum-was the tetraploid series, and that it is an allotetraploid species of hybrid origin, with the diploid species as one parent. The diploid species was then named-P.-appalachianum. The other parent of-P.-virginianum-was found to be-Polypodium sibiricum. The tetraploid of hybrid derivation tolerates warmer climates than either parent.