Identifying My Mystery Fern at Night in January

I have a mystery fern in my side yard shade garden. I got it this Fall for half price from Allisonville Nursery, and I love it. I was a little grossed out by the dark sori (the little black dots) but now I'm okay with them. I thought they looked like warts at first, I'm just not used to having dark sori. Sori I'm not sori!

Trying to identify a mystery fern, in January, at night... extra difficult!

Anyway, I love my little fern - it's actually still green right now even after being under about a foot of snow for a week and withstanding single digit temperatures. There's only one problem, I don't know what kind of fern it is because it didn't have a tag, and that bothers me - it gets in my head and it bothers me.




So I tried to find out! The problem is there are tons of ferns out there and they all look the same, until you learn more and look closer. Some basic background on ferns is extremely helpful. So I surfed the web for about 2 hours and here is what I came up with...

Prominent, dark, non-marginal sori - and I know it's hard to tell with the pinnule slightly bent but the 2nd is longer than the 1st here on the bottom right.

The Connecticut Botanical Society website was an amazing help, and so was TrekOhio! I quickly narrowed it down to some kind of wood fern because it has prominent sori and jagged pinnules. The sori aren't on the edges of the leaf, so I could eliminate marginal wood fern.

Sometimes the stipe (the portion of stem that goes from the root to the leafy fronds) is important to identification, here not so much. Notice here some of the fronds don't have sori - what's the deal with that? If some of the fronds are sterile that makes this dimorphic even though wood ferns are usually monomorphic.

Fern symmetry can also be important to determine identity... here in January at night... I would classify this as messy

This still left 3 possible close calls! Was it the spinulose wood fern, mountain wood fern, or evergreen wood fern? What the heck? They sounded so similar. It gets even more technical...

"The difference concerns the configuration of the basal pinna. If the first lower pinnule is opposite and longer than the second, it is spinulose. If the first lower pinnule is alternate and longer, it is mountain. If the second lower pinnule is longer than the first, it is evergreen." - Hiker's Notebook (http://www.sierrapotomac.org)

 Similarly, this description was consistent:

"One way to distinguish them is to look at the lowest pair of leaflets (pinnae). On spinulose woodfern, the lower subleaflets (pinules) closest to the main stalk are longer than the next set further out. On intermediate woodfern, the second set out from the main stalk is usually the longest." - Connecticut Botanical Society

So here is my evidence for Dryopteris intermedia, the evergreen wood fern: it has (1) dark visible sori, (2) jagged pinnules, and (3) the second lower pinnule is longer than the first, and (4) the fern is green in January so the 'evergreen' fern makes sense, while the Dryopteris spinulosa is listed as deciduous.

Here is my evidence against it being an intermediate wood fern: (1) not symmetrical in growth habit, (2) some sterile fronds means it's not monomorphic.

What do you think? Did I get it right? Feel free to offer your comments below!

Update: After spotting an identical looking fern at a garden show, I now believe this fern is Dryopteris erythrosora and possibly as specific as Dryopteris erythrosora 'Brilliance' - I will be able to get some more info when my fern starts growing this spring because new fiddle heads are supposed to be pink.