The fern genus Asplenium is well known for its hybridization capacity, especially in temperate zones.
The Appalachian hybrid complex in Asplenium is a polyploid complex composed of three diploid species, three allotetraploid species formed by hybridisation and chromosome doubling from the former, and assorted diploid, triploid and tetraploid hybrids between the six species.
Their chromosome complements are abbreviated "MM", "PP" and "RR", respectively.
At some point in the past, each of the sterile diploid hybrids experienced a chromosome doubling event that made them fertile allotetraploids; allozyme analysis shows that this happened on several independent occasions for A. montanum × platyneuron and A. montanum × rhizophyllum.
These doubling events gave rise to the following tetraploids: Since these allotetraploids are fertile, they are capable of crossing with each other and with the three diploid species to form the following sterile triploid and tetraploid hybrids, most of which are quite rare and occur sporadically where their parents' ranges overlap: 19 hybrids within the genus have been described from New Zealand, but have not been given binomials.