Stroud Preserve: Ferns
By Russell Rogers, Stroud volunteer
Spring is a time when most people look forward to seeing the explosion of colors of all the wildflowers and songbirds of our area. One look at a singing Yellow Warbler or a hillside full of Virginia bluebells, and the gray doldrums of our long winters suddenly become a distant memory. One reason these vibrantly colored elements of our countryside stand out so well is that they are cast against a sea of green. With so many brightly colored things to catch our eye this time of year, it can be easy to look past the vast variety of trees, grasses, sedges and ferns that serve as their background.
Ferns, and their allies, including horsetails, adder’s tongue and royal ferns, are an incredibly diverse group of plants found in just about every habitat type in Pennsylvania. The Stroud Preserve is a great place to see many of these, most of which are easily viewable from the preserves many trails.
From the Creek Road parking lot it is a very short walk to what is probably the preserve’s most strange and interesting fern, the Purple cliffbrake. It can be found growing on the stone walls of the bridge that goes over the East Fork of Brandywine Creek.
Purple cliffbrake Pellaea atropurpurea (L.) Link
This fern is fairly uncommon and found only in the eastern portion of the state. Ferns, having neither flowers nor seeds, reproduce via spores that are held and released from the underside of a fern’s leaves. Only some of a fern’s leaves carry the spores. At first glance, it is difficult to tell which of a fern’s fronds bear the spore-producing leaves (“fertile” leaves/fronds), and which fronds are non-spore-producing (“sterile”). The Purple cliffbrake’s fertile and sterile leaves, however, are so different in shape and color that, if it weren’t for their proximity to each other, you would think the fronds belonged to separate plants. That is to say, Purple cliffbrake exhibits “frond dimorphism”. The Purple cliffbrake prefers limestone cliffs and other rocky outcrops and, occasionally, the stone walls of old barns and bridges. It is also unusual in the way of ferns because its fronds are evergreen and can be seen on the bridge year round.
Keep walking west down the road over the bridge, and on the right you will see a creek that has a large population of Sensitive ferns.
Sensitive fern Onoclea sensibilis L.
Some people assume that, because of their name, they fold up like a Venus flytrap when you touch them, and that would be a truly remarkable thing if it were true. Unfortunately, it is not. In fact, it gets its name because it is sensitive to extremes in temperature. In the cold snap that we had the other week, these ferns lived up to their name –the following day, the new fronds were brown and shriveled up.
From here, choose any of the preserve’s trails through the woodlands, and you will almost certainly see Christmas and Lady ferns. They are by far the most commonly encountered ferns in the preserve. Like the Cliffbrake, the Christmas fern is green all year long. In contrast to the thick leathery leaves of the Christmas fern, the leaves of Lady ferns are light and wispy, indicating their ephemeral nature. 
Christmas fern Polystichum acrostichoides
Lady fern Athyrium filix-femina
Be sure also to keep an eye out for some of the lesser known and harder to find ferns like Rattlesnake fern, Long beech fern, and Evergreen wood-fern, all of which can be seen within several feet of the preserves trails.
Rattlesnake fern Long beech fern Evergreen wood-fern
If you make your way around to the serpentine outcrop on the north side of the preserve, look closely in between the cracks in the rocks and you will see a few ebony spleenworts, one of the few ferns that can tolerate the serpentine environment. Lastly, don’t forget to take a broader look around. You might even see a vivid pink of a wild geranium or the neon orange of a Baltimore Oriole!
Ebony spleenwort Asplenium platyneuron (L.) Britton, Stearns & Poggenb.