The

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...

genus ''

Asplenium ''Asplenium'' is a genus of about 700 species of ferns, often treated as the only genus in the family Aspleniaceae, though other authors consider ''Hymenasplenium'' separate, based on molecular phylogenetic analysis of DNA sequences, a different ...

'' is well known for its hybridization capacity, especially in temperate zones.

Appalachian ''Asplenium'' hybrid complex

The Appalachian hybrid complex in ''Asplenium'' is a

polyploid complex A polyploid complex, also called a diploid-polyploid complex, is a group of interrelated and interbreeding species that also have differing levels of ploidy that can allow interbreeding. A polyploid complex was described by E. B. Babcock and G. Led ...

composed of 3 diploid species, 3 allotetraploid species formed by hybridisation and chromosome doubling from the former, and assorted diploid, triploid and tetraploid hybrids between the 6 species. The three diploid parent species are mountain spleenwort (''

Asplenium montanum ''Asplenium montanum'', commonly known as the mountain spleenwort, is a small fern endemic to the eastern United States. It is found primarily in the Appalachian Mountains from Vermont to Alabama, with a few isolated populations in the Ozarks ...

''), ebony spleenwort (''

Asplenium platyneuron ''Asplenium platyneuron'' (syn. ''Asplenium ebeneum''), commonly known as ebony spleenwort or brownstem spleenwort, is a fern native to North America east of the Rocky Mountains. It takes its common name from its dark, reddish-brown, glossy sti ...

''), and American walking fern (''

Asplenium rhizophyllum ''Asplenium rhizophyllum'', the (American) walking fern, is a frequently-occurring fern native to North America. It is a close relative of '' Asplenium ruprechtii'' (syn: ''Camptosorus sibiricus'') which is found in East Asia and also goes by the ...

''). Their chromosome complements are abbreviated "MM", "PP" and "RR", respectively. Three possible sterile diploid hybrids can form from their hybridization: *''A. montanum × platyneuron'' (MP) has been collected on very rare occasions. *''A. montanum × rhizophyllum'' (MR) is theorized to exist, but has never been collected. *''A. platyneuron × rhizophyllum'' (PR) is known as Scott's spleenwort (''

Asplenium × ebenoides ''Asplenium'' × ''ebenoides'' (Scott's spleenwort, dragon tail fern or walking spleenwort) is a hybrid fern native to eastern North America, part of the "Appalachian ''Asplenium'' complex" of related hybrids. The sterile offspring of the w ...

'') and is relatively common. In addition, ''A. platyneuron'' and ''A. rhizophyllum'', which have a more extensive range, hybridize with other spleenwort species outside the Appalachian complex. At some point in the past, each of the sterile diploid hybrids experienced a chromosome doubling event that made them fertile allotetraploids;

allozyme Alloenzymes (or also called allozymes) are variant forms of an enzyme which differ structurally but not functionally from other allozymes coded for by different alleles at the same locus. These are opposed to isozymes, which are enzymes that perfo ...

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: {, class="wikitable" , - !Common name !Scientific name !Parents !Chromosomes !Ploidy !Notes/Distribution , - , Wherry's spleenwort , '' Asplenium × wherryi'' , ''A. bradleyi × montanum'' , MMP , triploid , , - , , , ''A. bradleyi × platyneuron'' , MPP , triploid , Believed to have been collected once at an early date in

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

; the site is now destroyed. Also reported from

Sequatchie County, Tennessee Sequatchie County is a county located in the U.S. state of Tennessee. As of the 2020 census, the population was 15,826. Its county seat is Dunlap. Sequatchie County is part of the Chattanooga, TN– GA Metropolitan Statistical Area. Histo ...

. , - , Graves' spleenwort , '' Asplenium × gravesii'' , ''A. bradleyi × pinnatifidum'' , MMPR , tetraploid , , - , Trudell's spleenwort , '' Asplenium × trudellii'' , ''A. pinnatifidum × montanum'' , MMR , triploid , The Appalachians and the

Shawnee Hills The Shawnee Hills is a region of southern Illinois that rests mainly in an east-west arc roughly following the outline of the southern end of the Illinois Basin. Whereas Mississippian and Pennsylvania Age rock layers are deep beneath the soil su ...

. , - , Kentucky spleenwort , '' Asplenium × kentuckiense'' , ''A. pinnatifidum × platyneuron'' , MPR , triploid , , - , , , ''A. tutwilerae × pinnatifidum'' , MPRR , tetraploid , Created in culture. , - , Boydston's spleenwort , '' Asplenium × boydstoniae'' , ''A. tutwilerae × platyneuron'' , PPR , triploid , Havana Glen, Alabama , - , , , ''A. tutwilerae × rhizophyllum'' , PRR , triploid , Created accidentally in culture.

New Zealand hybrids

19 hybrids within the genus have been described from New Zealand, but have not been given binomials.

Other hybrid species

*'' Asplenium afghanicum'' ('' Asplenium dolomiticum'' × '' A. lepidum'' var. ''haussknechtii'') *''

Asplenium azoricum ''Asplenium azoricum'' is a fern from hybrid origin of the family Aspleniaceae, descendant of the Macaronesian ancestral fern ''Asplenium anceps''. It lives exclusively in the Azores, that is a strict endemic Azorean fern. Its fronds are coriaceo ...

'' ('' A. anceps'' × ?) *'' Asplenium × biscayneanum'' ('' Asplenium dentatum'' × '' A. verecundum'') *'' Asplenium × curtissii'' ('' Asplenium abscissum'' × '' A. verecundum'') *'' Asplenium majoricum'' ('' A. fontanum'' × '' A. petrarchae'') *'' Asplenium reuteri'' ('' Asplenium lepidum'' × '' A. trichomanes'') * Hybrid plants