Sunday, February 18, 2018

The Asplenium Ferns of Ohio

The world of ferns is diverse and ancient. Many of these spore-producing wonders are living fossils and have remained relatively unchanged over millions of years. They've found their place and function in nature and are content to sit back and admire their successes at this point. Or, at least that's how I like to romanticize it. Ferns also happen to be some of my favorite plants but for whatever reason have seen little time dedicated to them on here. I believe that's due for a change.

It's been a while since I last focused on a specific genera of Ohio native plants, too. So why not mix things up and spend some time in the pteridophyte zone and break down the seven extant species of spleenworts (Asplenium) indigenous to my home state. The Aspleniums are arguably my most beloved of all fern genera and can superficially look similar from a distance and even up close. They aren't a hard group to get wrap your mind around with a little help and practice. Which is why I'm here!

The seven extant species of spleenwort (Asplenium spp.) ferns to be found in Ohio

Worldwide there are hundreds of species of Asplenium, with a large majority of them restricted to the tropical regions of the globe. Here in North America we have 28-30 different species and only seven within Ohio's borders. All our spleenworts are small, delicate ferns with slender and somewhat lacy appearances. They also happen to be a promiscuous bunch with many naturally-occurring hybrids. In fact, many of the 'species' we have today are hybrid in origin. Through the millennia the sterile diploid hybrids experienced a doubling of their chromosomes to create fertile allotetraploids. An example is lobed spleenwort (A. pinnatifidum), an allotertraploid derived from the mixing of mountain spleenwort (A. montanum) and walking fern (A. rhizophyllum). I could spend an entire post on this fascinating, and admittedly complex process but let's keep things simple.

All Ohio Asplenium are more or less evergreen. They hang around through the winter months but don't look near as aesthetic or ideal in the harsher conditions. Don't be fooled though: these ferns are tough as nails! They have a tenacity and fight in them that's to be admired, for they choose some harrowing places to live.

Typical habitat for many species of Ohio spleenwort

When it comes to hunting spleenworts around here your best bet is to find some nice rock exposures in the S/SE/E sections of the state. The greatest spleenwort diversity and densities in Ohio are definitely in the unglaciated SE quarter. Almost all our species are rock specialists and will only be found growing in pretty predictable and specific situations. Some of these ferns prefer non-calcareous substrates like acidic sandstone, granite, or shale. Others stick to calcareous rocks and are restricted to the state's limestone regions. They occur in full sun to partly shaded conditions, with some preferring more mossy, mesic spots to others growing literally out of tight crevices and cracks in pure rock. I'll discuss each spleenwort's specific preferences in their profiles below.

For as tough as they all, they're still non-mobile organisms that can't get up and move if a spot becomes unsuitable. So when you're looking for these wonderful ferns try to find a more secluded and/or undisturbed rock habitat to visually scour. Rock climbing, popular hiking destinations with rude plucking fingers, and overly exposed areas typically have fewer ferns to admire. You'll know you're somewhere special when a rock face is just dripping with a diversity of ferns!

With all that being said, I'd like to jump into the species profiles. Each of the seven native taxa, and one naturally-occurring hybrid are featured below with photos, descriptions, range maps, habitat descriptions and some general pointers on where to find them. I've decided to list them in alphabetical order for sake of ease and organization. As usual, I don't write any keys as the experts have graciously done that already and how could I expect to do any better. For a great book on Ohio's (and the surrounding region) ferns, I could not recommend one more than Midwest Ferns: A Field Guide to the Ferns and Fern Relatives of the North Central United States by Steve W. Chadde. It's not expensive and readily available on Amazon. It's definitely become my go to for all my spore-producing needs.

Asplenium bradleyi  -  Bradley's Spleenwort

First up is Ohio's rarest of the ferns featured here, Bradley's spleenwort (A. bradleyi). It's an endangered [S1] species in the state and found in precious few places. It's an allotetraploid that arose as a hybrid between mountain spleenwort (A. montanum) and ebony spleenwort (A. platyneuron).

Bradley's Spleenwort (A. bradleyi) in situ

Bradley's spleenwort is a small, clumped evergreen fern that is restricted to sandstone and other non-calcareous rock. It does an incredible job of fitting into small fissures, cracks, and crevices where a spore was fortunate enough to land. It prefers dry, sunny sites with few other plants growing on the sheer rock faces.

Close up of the fronds of Bradley's Spleenwort
View of the sori of Bradley's Spleenwort

Bradley's spleenwort has a relatively short, dark red-black stipe (stem before the 'leaves') that transitions to a green as you approach the rachis (stem with the 'leaves' or pinnae). Each pinnae is born on a very short stalk with a sharp-toothed to wavy margin. The spore-containing sori are found on the undersides of the pinnae on fertile fronds. They're paired up along the midrib and mature from a gold color to blackish brown. The only Asplenium you're likely to confuse Bradley's with is mountain spleenwort, which makes sense as one of its parent species. However, Bradley's fronds are long and narrow, while mountain's fronds are more deltoid in shape and their pinnae are on longer stalks. Compare with the photos below.

North American distribution of Bradley's Spleenwort (courtesy: BONAP)

Bradley's spleenwort is primarily a species of the Appalachians and curiously the Ozarks region of Missouri and Arkansas. Here in Ohio it's only ever been located in a handful of southeastern counties and currently considered extant in Fairfield and Washington counties. Two of the known sites are thankfully on preserved land but due to their rarity and fragility their locations will not be shared.

Asplenium montanum - Mountain Spleenwort

The next species on this treatment of Ohio's spleenworts is the mountain spleenwort (A. montanum). I'm of the opinion that this fern is the most attractive and intricate of our spleenworts. It can form large aesthetic clumps if happy and really impress anyone who notices as they walk by.

Mountain Spleenwort (A. montanum) in situ

Much like its aforementioned Bradley's kin, the mountain spleenwort is a non-calcareous rock specialist. It will often be about the only vascular plant seen growing in its rock face habitat. Mountain spleenwort is a locally common species where impressive sandstone rock formations are prevalent and relatively undisturbed. The Hocking Hills region and Lake Katharine state nature preserve in SE Ohio are excellent places to see this fern in situ.

Mountain spleenwort doing what it does best
Mountain Spleenwort

Appearance wise mountain spleenwort isn't too hard to discern from Ohio's other Aspleniums. It grows in concentrated clumps with oblong-triangular shaped fronds that appear greenish-blue and leathery. The pinnae sit on noticeable stalks, with each containing some lobing, especially the lowermost pairs. The sori mature brown and are scattered irregularly on the undersides of mature fronds. Mountain spleenwort is additionally one of the more scandalous Aspleniums and regularly hybridizes with other species, especially lobed spleenwort.

North American distribution of Mountain Spleenwort (courtesy: BONAP)

Looking at mountain spleenwort's distribution map it's easy to notice its a fern of the Appalachian mountain range. Here in Ohio it is restricted to the unglaciated Allegheny Plateau where it occurs on a variety of non-calcareous rock, especially sandstone. As mentioned, the Hocking Hills and Lake Katharine areas are excellent places to seek out this fern.

Asplenium pinnatifidum - Lobed Spleenwort

Continuing on is another species in the Appalachian spleenwort complex, the lobed spleenwort (A. pinnatifidum). It arose as a hybrid between mountain spleenwort and walking fern (A. rhizophyllum). 

Lobed Spleenwort (A. pinnatifidum) in situ

Keeping with the trend of the ferns shared so far, lobed spleenwort is another one that prefers non-calcareous rock substrates. It is a bit more forgiving in the shade and can occur in both dry and more moist conditions. Here in Ohio it's most commonly seen on sandstone but can grow on gneiss as well.

Lobed Spleenwort close up
Lobed Spleenwort in situ

The fronds overall are lance-shaped, like their parent walking fern with a long-tapering tip. The lower sections are usually cut into the pinnae-like lobes. It should pointed out that lobed spleenwort can vary greatly in just how 'lobed' its fronds are. I've observed extremely lobed fronds, I've seen fronds that didn't have nearly any lobes, and everything in-between. Regardless of how many lobes a frond may have it's most important to look at the base of the lobe and confirm there is no stalk and the lobe is firmly attached to the rachis. Observe this feature in the accompanying photos. Lobed spleenwort is usually a more solitary-occurring plant but large colonies can sometimes be found.

North American distribution of Lobed Spleenwort (courtesy: BONAP)

Lobed spleenwort's distribution looks strikingly similar to mountain spleenwort's. It ranges further west and is more prevalent in Ohio, too. Anytime you see some exposed sandstone rock formations is a good place to take a peek. With such overlaying ranges and shared habitat preferences it's no surprise lobed and mountain spleenwort will often grow in association with one another. And when that happens things can get a bit wild so to speak...

Asplenium x trudellii - Trudell's Spleenwort

As I pointed out in the opening sections of this post the genus Asplenium is notorious for producing hybrids. There are over 20 accepted spleenwort hybrids in North America, with no fewer than six having been collected in Ohio. The most common of all is Trudell's spleenwort (A. x trudellii), a sterile triploid formed from the crossing of mountain and lobed spleenwort.

Trudell's Spleenwort (A. x trudellii) in situ

Trudell's spleenwort is intermediate in appearance between its two parents but definitely has more of a lobed spleenwort look to it than mountain spleenwort. It will come as no surprise that it occurs in the same habitats as its parents and often nestled right in with 'pure' strains of both. 

Comparison: mountain spleenwort on L; Trudell's spleenwort in the middle; lobed spleenwort on the R

While in the Hocking Hills a ways back, I plucked a couple fronds of Trudell's, mountain and lobed spleenworts for a comparison shot. The key feature to know you have Trudell's is to find the lower pinnae with conspicuous stalks. Recall that lobed spleenwort, no matter how lobed it is will lack stalked pinnae entirely. The middle fronds show that feature perfectly. Also take note that the fronds of Trudell's are larger than either of its parents. Many times hybrid "species" are larger than their parents due to something called 'hybrid vigor' or heterosis. That can be another clue you have Trudell's spleenwort if you see an exceptionally lobed and monster-sized lobed spleenwort.

North American distribution of Trudell's Spleenwort (courtesy: BONAP)

For reference is a distribution map of known collections of Trudell's spleenwort in North America. Obviously, it's restricted to where both parents occur together and if you'd like to sniff some out, I'd recommend the aforementioned Hocking Hills and Lake Katharine locales. I've personally seen nice examples of this hybrid alongside its parents at both locations.

Asplenium platyneuron - Ebony Spleenwort

This next species of fern is undoubtedly Ohio's most common Asplenium and found throughout most of the state. Ebony spleenwort (A. platyneuron) is also on average the largest of our spleenworts.

Ebony Spleenwort (A. platyneuron) in situ

Ebony spleenwort distinguishes itself from the rest of its Asplenium kin in several ways. Most noticeable and previously mentioned is its size. This fern can appear in a smaller fashion but larger fronds can grow well over a foot long. Another factor separating it from other spleenworts is it's just as likely to be found growing in soil as it is on rock. Most all other Aspleniums featured here are restricted to rock substrates. With variety of substrates comes a variety of habitat choices, too. You can find it in open woodlands, along streams, in old fields and clearings, and even growing in sidewalk cracks and on building foundations.

Ebony Spleenwort (A. platyneuron) in soil
Ebony Spleenwort on rock with smooth cliffbrake (Pellaea glabella)

Ebony spleenwort is a pretty easy species to identify even at a distance by its typically erect growing fertile fronds. The sterile fronds are usually more prostrate and evergreen, while the vertical fertile fronds wither in the winter months. The stipe is quite short before the pinnae appear. Both the stipe and rachis is smooth, shiny and a reddish or purple brown color. The pinnae are paired up in an alternately arranged fashion up the rachis. The lowermost pairs are quite small and increase in size as you go up the rachis with the frond being largest/widest in the upper third.

North American distribution of Ebony Spleenwort (courtesy: BONAP)

Ebony spleenwort ranges widely throughout eastern North America and occurs is just about every county in Ohio. It's mostly absent from the glaciated lake plain of NW Ohio. I encounter is most often in early-mid successional mesic woodlands in my area of the state.

Asplenium rhizophyllum - Walking Fern

Of all the Asplenium ferns I'll share on here, I don't think you'll find one as unique and charming as the walking fern (A. rhizophyllum). Older literature will place it in the genus Camptosorous but modern treatments have it rightfully in Asplenium. Which makes sense considering it readily hybridizes with other spleenworts.

Walking Fern (A. rhizophyllum) in situ

In a departure from most of the Aspleniums we've covered so far, the walking fern is strictly a limestone lover. If you find yourself in a cool, moist place with exposed limestone bedrock covered in moss, I'll bet you'll find some! The Edge of Appalachia preserve system and Clifton Gorge state nature preserve are places you'd be hard pressed to not see walking fern at.

Walking Fern on a moss-covered limestone boulder
Walking Fern

Another departure from the previous spleenworts is walking fern's tendency to form large, sprawling colonies in prime conditions. This is achieved by a frond's ability to form a plantlet at the end of its long-tapered tip. This plantlet will root and subsequently grow into a new plant and clone of the original. This allows the fern to, ahem...'walk' across its substrate. How neat is that!

North American distribution of Walking Fern (courtesy: BONAP)

Walking fern isn't nearly as common as the distribution map above infers. Due to its habitat specificity you're only going to find it in certain situations and they can be rather isolated. However, it's still not by any means a rare find and once you get the eye for its haunts you'll come across it with regularity.

Asplenium ruta-muraria - Wall-rue

We've come to the penultimate Asplenium species on this treatment of Ohio's spleenworts. It also happens to be my personal favorite of them all! The wall-rue (A. ruta-muraria) is a state threatened [S2] species in Ohio and only to be found in a handful of southern counties. It's certainly as rare as it is cute.

Wall-rue (A. ruta-muraria) in situ

The dainty and delicate wall-rue is another limestone lover and only found growing on shaded dolomite slump rocks, boulders, and cliff faces in Ohio. Due to such habitat specificity you're only going to see it in special places where its necessary bedrock requirements are met. The Edge of Appalachia preserve system and its plethora of dolomite is your best bet at spotting some in Ohio.

Wall-rue in the hand
Wall-rue on a dolomite boulder

Wall-rue's small and lacy appearance, as well as its unique habitat preferences make it a pretty easy fern to identify. The fronds and its bluntly-toothed pinnae are deltoid in shape and appear rather leathery. This fern can range from dark green to a blue-green color, which I find to be extra beautiful. The photo above of an exceptionally large fronds with your blogger's hand behind it gives a great opportunity to study its features and shape.

North American distribution of Wall-rue (courtesy: BONAP)

Wall-rue is most common along the central spine of the Appalachian Mountains with some outlying distributions to the west. It strangely reappears hundreds of miles disjunct to the north in the Straights of Mackinac region and the Bruce peninsula, where I've seen it on dolomite bedrock on Flowerpot Island.

Asplenium trichomanes - Maidenhair Spleenwort

The seventh and final species of Ohio Asplenium I have to share is the maidenhair spleenwort (A. trichomanes). It's another small, dainty species that comes across as extra charming when one finds it in the field.

Maidenhair Spleenwort (A. trichomanes)

Maidenhair spleenwort is another rock lover but interestingly can't seem to make up its mind whether it prefers calcareous or acidic, non-calcareous substrates. In Ohio you can find it on both types of rock, but the limestone-loving stuff is definitely more rare. Experts treat this spleenwort with two subspecies depending on its substrate choice. Those found growing on acidic sandstone are A. trichomanes subsp. trichomanes; those found on limestone are subsp. quadrivalens.

Maidenhair spleenwort on limestone (subsp. quadrivalens)
Maidenhair spleenwort on sandstone (subsp. trichomanes)

Like a majority of Ohio's spleenworts, maidenhair isn't too hard a species to discern from the others. It grows in tight clumps in cracks/crevices on slump rocks, boulders, and cliff faces. The stipe/rachis is smooth and a dark purple-brown color. The little orbicular pinnae are oppositely paired up and usually a pale green to greenish-yellow color. It typically occurs as sporadic individuals but I have seen it grow in sizable clumps, too.

North American distribution of Maidenhair Spleenwort (courtesy: BONAP)

Maidenhair spleenwort is the most wide-ranging of Ohio's Asplenium species and has been collected from just about every contiguous state. The previous six ferns have been restricted to east of the Mississippi River, but this one continues on westward and occurs in the southern Rockies and Pacific Northwest. In select areas of its range (NE, N Great Lakes and PNW), you may come across the green spleenwort (A. trichomanes-ramosum or A. viride). It looks nearly identical to the maidenhair and grows in the same habitat, even growing in association, but the green spleenwort has an entirely green stipe/rachis. Recall the maidenhair's is a dark purple-brown. Green spleenwort is much more uncommon and a celebrated find here in the east.

Asplenium resiliens - Black-stemmed Spleenwort

To wrap things up, I wanted to touch on an eighth and final spleenwort species that should be mentioned and included. The black-stemmed spleenwort (A. resiliens) was collected a single time in Ohio back in 1900 and has yet to be seen again. The collection site was in southern Adams Co., where its preferred habitat of sunny calcareous bedrock exposures, slump rocks, and cliff faces are quite common. It looks strikingly similar to the ebony spleenwort (A. platyneuron) and takes a pretty keen eye to notice the differences. Black-stemmed spleenwort has a pure black, glossy rachis; pinnae that are more or less oppositely arranged vs ebony's alternate arrangement; and the pinnae of black-stemmed are more or less entire vs ebony's wavy/toothed margins and the presence of a little auricle near the pinnae's stalk.

North American distribution of Black-stemmed Spleenwort (courtesy: BONAP)

Black-stemmed spleenwort is a species of the southeastern and south-central US, and isn't uncommon just south of Ohio's border in central Kentucky. It stands to reason this species could still be lurking on some isolated, over-looked rock in extreme southern Ohio and the romantic in me would like to think it can and will be rediscovered one day.

I hope you've enjoyed this look into the Asplenium ferns of Ohio! Like I've mentioned they are some of my most cherished ferns and a group that while not too difficult to learn still deserved some light shed on them. I hope this post will inspire you to get out and see these spore-producers for yourselves and perhaps take the time to become better acquainted with them. I'm sure many have walked right past them and not taken much notice before. Even better is you don't have to wait for spring due to most all species we have being evergreen! Thanks again for tuning in and happy botanizing!

- ALG -


  1. Excellent post, far better than any other I've ever seen about group of ferns. Thank you.

  2. NICE! BTW - this made me think of Den P.