Creeping Fragile Fern (Cystopteris protrusa) - ID Methods and Data Collection

Creeeping Fragile Fern (cystopteris protrusa)
Photo by Brad Sylvester, copyright 2011, all rights reserved

The plant species for today turned out to be the creeping fragile fern (Cystopteris protrusa), but it was a long two-day journey for me to figure it out. By the way, it’s also called Lowland Brittle Fern, Southern Bladder Fern, and Lowland Bladderfern. For me, identifying the species of the plants that grow in my yard is going to be much more difficult than identifying the animals that live in my yard as I do on my other blog: What Lives in my Yard. I could start off with very easy things like some of the big trees, the garden vegetables (whose names I can read from the seed packets), or some of the perennial flowers, but I want to develop some skills here and find reliable reference sources while I’m conducting this extended bio-survey. So today, I’m kicking it off with a fern, and detailing the process I went through to try to figure out what it was. A good field guide would have helped.

To start with, I chose a wild plant growing in my yard, one that I believe to be native to the region. It is an attractive forest edge border plant. I definitely want to keep it growing where it is and may even think about establishing it in additional areas.

Ordinarily, I’m going to include just one or two photos of each species that I record, because my storage space is limited. However, the first entry is going to be picture heavy, because I’m going to show a wide variety of traits that I captured in hopes of having enough information from which to draw a conclusion about this ferns’ true identity.

Gathering Data about Plants in the Field

Ferns along the forest edge
Photo by Brad Sylvester, copyright 2011, all rights reserved

First, where does it grow? As you can see from the picture to the right, it grows along the forest edge, but looking around my yard, I see that it only grows on the shady side. In other words, the woods are to the south of the ferns and the open yard to the north. That means the ferns are never exposed to bright, direct sunlight. As you can see above in a photo taken at about 1:30 pm on July 20, even at midday, the ferns are in shade or, at most, dappled sunlight. These ones happen to be near the edge of a seasonal brook, but I don’t know whether that is coincidental or not.

Next, I look at the individual leaves and the pattern in which they grow from the stem. This photo shows that they alternate off the main stem. One grows on the left side then a little higher on the stalk one grows from the right side.  For many plants, that’s an important clue. We also notice that other than these complex leaves, there are absolutely no side branches.

Leaf detail of creeeping fragile ferm (Cystopteris protrusa)
Photo by Brad Sylvester, copyright 2011, all rights reserved

These are complicated leaves. They almost resemble fractal patterns in their complexity. Eventually, when we narrow it down to some likely candidates, we should be able to match this pattern up for an exact match. We also note that although the overall shape of the frond is like a triangle, widest at the base and narrowing as it goes toward the tip, the lowermost 2-3 pairs of leaves are a bit shorter than those nearer the center of the plant breaking the true triangular shape.

Meanwhile, from my experience in growing up as a curious young boy in the woods of New England, I know that many ferns have distinctive spore structures on the underside of each leaf. Flipping this one over, I see that it does. These little white dots will each release spores that will fall to the forest floor or drift on the wind, or the back of some furry animal, until it reaches a suitable place to grow. True ferns do not have seeds at all, they reproduce with spores. The shape, arrangement, color and size of these will also help us identify this fern.

Sori of the creeping fragile fern (Cystopteris protrusa)
Photo by Brad Sylvester, copyright 2011, all rights reserved

Individual stems lead from the soil, not clustered stems
Photo by Brad Sylvester, copyright 2011, all rights reserved

What else can we see? At the base of each plant, a single stem emerges from the ground. These ferns don’t grow in clusters with many stems coming from a single base. Honestly, though, I don’t know what a fern’s root system looks like. Is there a bulb down there that stores energy through the winter? Are the roots like any normal plant? Let’s have a look. Carefully digging with my fingers so that I can feel the roots as I go and not damage them beyond all recognition, I find a surprise. The stem of the fern forms a perpendicular attachment to a horizontally running root.  Ah-ha! Although the fern is capable of reproducing through the dispersal of spores, it seems that might just be a back-up plan. Carefully following the “runner” or thick horizontal root, I come to another stem and another fern. Although they look like separate plants from above ground, they are, in fact, parts of the same larger plant.

Rhizome of Cystopteris protrusa showing next year's buds
Photo by Brad Sylvester, copyright 2011, all rights reserved

The other end of this runner heads out toward the lawn. Let’s see what happens there. Ah-ha again! We see a number of tiny branches, also in an alternating pattern, each with a little green bud-like formation at its tip. These are new ferns waiting to break through the surface.  If I didn’t mow the edge here would the ferns keep marching out into the lawn? Would they grow even in the sunlight? Probably not in the full sun, but they’d push the edge and might do ok in the spring and fall when the sun is at a lower angle and the shady area is extended further out into the yard. The root system might extend itself this way for a considerable distance under the lawn, just hoping that one of those underground branches will break through the surface in an area where it can thrive.

Communal Ferns

Which brings up another interesting question: is this whole patch of ferns actually just one plant? Does it grow almost as a colony originating from one single interconnected root system? I might, in fact, only have one fern in my yard, although it covers several hundred square feet. If they are all a signal plant, that also tells us something about its vulnerability to environmental toxins. In theory, an application of a powerful systemic herbicide in one part of the yard might be transported through the runner system to kill an entire patch of ferns where only one or two ferns were actually sprayed.

Similarly, a fungus or bacterial infection might also spread through this underground piping network to take out a whole patch of ferns fairly quickly. If we saw that happening, we might use a shovel to sever the underground runners between healthy areas of the fern patch and unhealthy areas. Then physically dig out and remove the bad part of the colony and hope that whatever it was hadn’t yet reached the rest of the root system.

If we were chemically treating a fungus infection we’d want to make sure that we spray the entire patch rather than just the visibly affected area to prevent it from traveling through the runners to an untreated area. Mind you, this is just conjecture on my part, and would need to be tested experimentally for confirmation.

Fern Propagation

By the way, if we wanted to propagate this very attractive fern as a landscape border or a shady ground cover, we’d dig up and cut a section of the root and bury it in the area where we wanted it to grow. I’m not sure whether we’d need an end piece with the tiny ferns ready-formed or whether any section of the root would be viable. Again, that’s an experiment waiting to happen. I expect that the end piece with the buds would work best and produce new ferns faster and more prolifically, but any significantly sized section of the root would also survive and begin forming buds as well. Just guessing, though.

Anyway, sorry to get distracted, but that’s part of the reason why I’m conducting this bio-survey, to discover things I didn’t know about the things that live and grow right in my own backyard. So for identification purposes we know:

1)      It produces spores from the underside of the leaves and we have images of the sori (a cluster of spore-producing structures).

2)      It has a single stem with alternating leaves growing from it.

3)      We have an image of the exact shape of the leaf.

4)      We know that it reproduces through rhizomes or underground roots and we know what those roots look like.

5)      We know what kind of habitat it likes.

6)      We know what part of the country it lives in.

Is that enough to identify it positively? I think so. First, I’m going to assume that I know it’s a true fern. So let’s start climbing the taxonomy tree. Searching the Internet, I find the University of Michigan’s Sustainable Urban Landscaping Information Series (SULIS) Ferns page. I’m not doing urban landscaping, but it stands to reason that sustainable landscaping would use native plants that grow naturally in the region and habitat which is to be landscaped.

From the information provided on the SULIS page, I’m going to rule out three of the four classes of ferns. What I have is not Psilotopsida of which the only surviving species is the whisk fern. It is not Lycopodiopsida which is comprised of spikemosses, clubmosses and quillworts. It is definitely not Equistopsida which as you might guess contains only horsetails.

That leaves Polypodiopsida (Pteropsida for you Latin-philes). These are the true ferns with 9 sub-classes, 25-300 genera (the plural of genus), and over 12,000 species. Sigh. By the way, SULIS has a page with information about fern propagation which confirms some of my rhizome cutting conjecture, and also reminds me that fern leaves are called fronds, and the spore cases on the underside are called sori.

Let’s get back to our taxonomy. Pteropsida is the class of true ferns within the phylum Pterophyta. I spent some time, unsuccessfully looking for an identification guide online. I’ll need to pick up a good fern field guide. Meanwhile, using Wikipedia, as much as it isn’t a primary research source, I find seven sub-classes: Osmundales, Hymenophyllales, Gleicheniales, Schizaeales, Salviniales, Cyatheales, and Polypodiales. Now I can search each of those and look for enough description to either include or exclude the fern I found in my yard from each subclass.

Wikipedia says 80% of today’s ferns fall into Polypodiales, so let’s start there. Searching again, I find the University of Wisconsin’s  Robert W. Freckman Herbarium page on fern identification, which drills down a bit lower than Polypodiales. Out next choice is between Families. I think my fern is a member of the Dryopteridaceae family, but it’s clear that to go any further, I’m going to need a vocabulary lesson to figure out what terms like rupestral, scandent, dictyostelic, glabrous, pinnatifid, acrostichoid, and too many others to list all really mean. The photos on the site are not sufficient for clear cut identification.

So let’s call it day and come back to this one another time.

Fern Identification Day 2

I came back to the problem of identifying this fern a day later with a fresh idea for searching for online identification guides and it bore fruit immediately -- quite unlike ferns themselves… I finally found a fern identification key at the University of Wisconsin – Green Bay.  It’s on the Herbarium page of the Cofrin Center for Biodiversity. As it asks about specific characteristics being present or not, it includes links on the key terms describing what each is and showing photographic examples. Exactly what I need. A virtual Fern Identification for Dummies. Consequently, it also helps me to learn the terms by using the built-in glossary. This will be my primary resource for fern identification.

At Last! Creeping Fragile Fern

By drilling down through their binary identification system I believe the fern I photographed to be of the genus Cystopteris. One species of that genus, Cystopteris protrusa commonly named the creeping fragile fern, seems to be the most likely candidate as it has some keys distinctions from other Cystopteris species.

1) The creeping fragile fern prefers to grown on soil rather than rocks.

2) It is the only species of the Genus in which the rhizome extends out past the last frond and contains buds for the following year’s fronds.

3) Its range includes New England and it is quite common.

It is the second characteristic which, to me nails the identity as Cystopteris protrusa. You’ll remember that I remarked about the rhizome extension and underground buds. This turned out to be a good exercise, a strong learning experience, and it really highlights the need for thoroughness in the field. I literally had to dig a little deeper to find the characteristic that led me to a good identification on this species.  Genuine curiosity is your best tool for exploration.

At present, I am not abotanist. I've had zero training. I am however, very curious, and quite persistent. In a year from now, I'll be pretty darn good at idenitfying plants by site in the field. If you faollow along with me on this blog and put what you lean into practice, you just might be too.

Cystopteris protrusa Propagation Revisited

By the way, based on the fact that we know the buds represent the following year’s ferns, I expect that to propagate the creeping fragile fern, this terminal portion of the rhizome would need to be transplanted. This may, or may not, hold true for other species of the genus.