Suspected intergeneric hybrid of Polystichum munitum and Arachniodes simplicior

There is a particular area behind my garage where I keep potted plants which has proven quite a nice spot for growing ferns, to the point where I'm regularly finding self sown ferns showing up in pots I hadn't planted them in as well as in the surrounding soil.  Until now, all of these "volunteer" ferns have been one of two native species which had dropped an abundance of spores in the area since I had intentionally been growing potted specimens in that area.  These two native species are Polystichum munitum (western sword fern) and Athyrium filix-femina ssp. cyclosorum (western lady fern).  

Recently, I went through multiple pots full of young self sown ferns to separate them out for potting on into individual pots.  While doing so, one young fern which at first glance appeared to be Polystichum munitum became quickly apparent as an anomaly.  Among its otherwise typically pinnate fronds were two which were subtley bi-pinnate!  That is to say that in addition to the primary vein lined with serrated leaflets on either side, each of these two atypical fronds had also produced branches (one with a single branch and the other with a pair of branches) along the main leaf vein which were significantly more developed than the leaflets above them on the main vein.  These "branches" appear like reduced versions of the primary main vein with their own pinnate leaflets along their lengths.  

Initially, I assumed it was some sort of mutation, but after contemplating it off and on over following days, I realized that given the location, this young fern was far more likely the result of unintentional intergeneric hybridization than simply the result of non-hybrid mutation.  In addition to the two bi-pinnate fronds mixed among the more typically pinnate fronts, I also noticed (upon re-inspection) that there were additional distinguishing features.  The out-facing "thumb" at the base of each leaflet which is typical of P. munitum was present, but of reduced prominence and more rounded.  Additionally, the tip of each leaflet along with the tip of frond were consistently less sharply pointed than those of the neighboring P. munitum plants.  

Before deciding what the most likely other parent of this hybrid was, I compiled a list of the other fern species I have grown in that area which could have contributed their spores to the mix.  Other ferns I have grown in this spot have been:

• Blechnum spicant (deer fern) - Ruled out as a possible parent because I have only had young potted specimens in that spot which produced sterile fronds, but no fertile spore producing fronds.
• Matteuccia struthiopteris (ostrich fern) - Ruled out as a possible parent because I have only had young potted specimens in that spot which produced sterile fronds, but no fertile spore producing fronds.
• Adiantum aleuticum (western maidenhair fern) - Given consideration, but too many reasons exist to rule it out as an option.  Too distantly related to have a likelihood of intergeneric compatibility.  Frond branching of a totally different pattern than present in the hybrid specimen, plus no other visual similarities.
• Polypodium glycyrrhiza (licorice fern) - Ruled out for not only being too distantly related for intergeneric compatibility, but also since the hybrid specimen did not show or even hint at showing any of the traits characteristic of this species.
• Dryopteris lepidopoda (sunset fern) - Exceptionally unlikely despite being within the same subfamily as Polystichum muntum since only a single young specimen was kept there briefly and no traits of the found hybrid show any traits which point to it as a parent.
• Dryopteris affinis 'Cristata the King' (male fern) - Though also in the same subfamily as Polystichum munitum, only very young plants were present in this location and were not likely to have dropped any spores.  Additionally, no traits of the found hybrid point to it as a likely parent.
• Woodwardia fimbriata (giant chain fern) - Ruled out as only a single young specimen was kept in this spot which was unlikely to have produced any spores.  Plus the found hybrid does not possess any traits which point to this species as a parent.
• Coniogramme emeiensis (bamboo fern) - Ruled out as only one specimen was present in this area for a short time before it died.  It is both unlikely to have contributed spores, but also no traits of the found hybrid point towards this species as a likely parent.
• Arachniodes simplicior 'Variegata' - Though surprising, there are a lot of reasons to suspect this as the "other" parent of the found P. munitum hybrid.  Admittedly, only a single specimen was present in this spot for approximately one growing season.  However, it was likely mature enough to contribute spores.  Additionally, like Dryopteris, Arachniodes is also in the same subfamily as Polystichum (Dryopteridoideae), making it closely enough related to entertain the possibility of intergeneric compatibility.  Also, both P. munitum and A. simplicior possess the same diploid chromosome count of 2n=82 which would facilitate more smooth chromosome pairing in a hybrid of the two.  While these points indicate that this hybrid pairing could be possible, it is a tell tale sign that A. simplicior produces fronds which often have lower leaflets which develop enough to create a branched appearance with further leaflets of their own for a bipinnate appearance.  Once taking this species into consideration, it becomes very easy to look at the found hybrid and see that the various aspects of its appearance do in fact look intermediate between P. munitum and A. simplicior!

With a bit of Googling I am aware that intergeneric hybrids within the Dryopteridoideae subfamily are already known to occur, existing both in the wild and in cultivation.  While these known hybrids seem to typically be between Polystichum and Dryopteris, I believe that this is very strong evidence in support of my found hybrid being the result of the two parents I suspect it to be based on the combination of physical presence on site along with observable morphology.

I know this blog post by no means counts as an official scientific publication which could be used to document a new botanical name for this hybrid, but for fun I propose using the new hybrid specific epithet of ×Polystachniodes municior to reference this new and previously unknown intergeneric combination of Polystichum munitum and Arachniodes simplicior.