Asplenium hybrids

The fern genus Asplenium 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 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), ebony spleenwort (Asplenium platyneuron), and American walking fern (Asplenium rhizophyllum). 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) 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 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:

Common name Scientific name Parents Chromosomes Notes/Distribution
Bradley's spleenwort Asplenium bradleyi A. montanum × platyneuron MMPP The Appalachians, Ozarks, and Ouachita Mountains.
Lobed spleenwort Asplenium pinnatifidum A. montanum × rhizophyllum MMRR The Appalachians and the Shawnee Hills.
Tutwiler's spleenwort Asplenium tutwilerae A. platyneuron × rhizophyllum PPRR Havana Glen, Alabama

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:

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; the site is now destroyed. Also reported from Sequatchie County, Tennessee.
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.
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
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