Fossils and fiddleheads: A look at some local species of fern and what makes them so fascinating

As a kid, I remember watching time-lapse videos of a flower blooming or of the sun racing across the sky. Of course, things don't happen that way in nature with one possible exception: sprouting, young ferns. I swear one fern “fiddlehead” I spot in the morning has grown inches by late in the afternoon.

Since fern fronds will be appearing soon, I'd like to introduce you to three species: maidenhair, sensitive, and ostrich fern. While they are all green, ferns differ from other vegetation such as trees and wildflowers. Let me explain.

Seeds vs. spores

As the old saying goes, mighty oaks from little acorns grow. Since ferns are nonflowering plants, they don't grow from acorns or any other nut, fruit, or seed. Ferns sprout from microscopic or tiny, dust-like particles called spores. Size is just one of the differences between seeds and spores.

Spores are tiny because they are unicellular while seeds are multicellular. Seeds contain nutrients for the growth of the developing plant embryos. Spores do not. With this reservoir of food, seeds are better able to withstand harsh conditions than are spores.

The food for the seed also attracts animals that eat the nuts and berries and help spread the seeds. Spores rely on the wind to get around. Interestingly, grazing animals rarely eat ferns. We'll come back to that. Lastly, spores require more moisture for germination than do seeds. This explains why most ferns are found in shady areas.

If present, the location and shape of spore bundles, called sori, can help identify a fern. With many fern species, the sori can be found under the edges of the leaflets. With other ferns the sori are on separate fronds. Just so you know, fungi also use spores to reproduce.

Fern terms

Since ferns are NON-flowering plants, we can't be using flowering plant terms to describe their parts now can we? Oh no. So here's a quick fern structure primer. I will first use the fern term followed, when appropriate, by the flowering plant equivalent in parentheses. A fern has a frond (leaf) on a stipe (stalk or petiole). The blade starts above the stipe and is divided into pinnae (leaflets) which come off the rachis (midrib) of the frond. The pinnae can be further divided into pinnules. Had enough jargon? On to three fun-named ferns.

Maidenhair fern

Maidenhair fern (Adiantum pedatum) is believed to have been named after its nearly black, shiny stipe and rachis. It is thought that these characteristic stalks reminded some of fine, dark root hairs. According to a German folk tale, a maiden fell to her death off a cliff after her lover was turned into a wolf. A spring appeared where she fell and her hair turned into a fern.

Maidenhair's fronds, which can grow to 16 inches in length, are arranged in a circular or horseshoe pattern. The wavy pinnules are only dissected on one side. Its sori are found on the underside, notched edge of the pinnules. The sori may be oblong to linear and are difficult to see since the leaf edge often curls over the spores.

This distinctive fern likes to grow in moist, shaded, somewhat alkaline soils and can be found across the Chicago area. Maidenhair's black stems sometimes disappear against a dark background and can give this fern an otherworldly appearance.

Sensitive or bead fern

This fern's name came from the fact that the sensitive fern quickly dies back after the first frost of autumn. It also is quite “sensitive” to drought and direct sunlight.

Not surprisingly, sensitive fern (Onocha sensibilis) is a denizen of swamps, marshes, bogs, wet woods, and along streams. This fern is relatively common in northeastern Illinois. It can grow to be 40 inches high. Unlike with more delicate and lace-like ferns, the fronds of sensitive fern look like they were cut out by a child using safety scissors. The margins have crude curves and wavy edges with little detail.

Interestingly, sensitive fern has two types of fronds, sterile and fertile. The paragraphs above refer to the sterile fronds. The fertile fronds are thinner and barely half as long. These fronds are covered with bead-like sori that earn this fern its other common name, bead fern. While the sterile fronds die back after the first frost, fertile fronds will turn brown but persist until spring when they release their spores. Be aware that sensitive fern fronds exhibit a wide range of sizes and shapes.

Ostrich or fiddlehead fern

At first glance, it is hard to believe that sensitive and ostrich fern belong to the same family of ferns. Ostrich fern (Matteuccia struthiopteris) is named after its sizable plumes, I mean, fronds. This reminds me that the word fern stems from the Anglo-Saxon term “fearn,” meaning feather.

Ostrich fern ranges in height from two to six feet. It grows in moist to wet woods and thickets. The plant does well in shade, partial shade, and sun. It also thrives in human landscapes and is often planted for decoration in shade gardens. In fact, the ostrich ferns we have at Stillman were transplanted from a house that was soon to be torn down. As you might have guessed, ostrich ferns can be found across our area.

Like sensitive fern, ostrich fern has sterile and fertile fronds. Unlike sensitive fern, the ostrich fern fronds have intricate patterns. The sterile frond is divided into pinnae which are, in turn, divided into pinnules. The frond is widest above the middle rapidly tapering to the tip.

The fertile ostrich fronds are bronze and half the height of the sterile ones. They have compact heads with extremely narrow pinnae. These fertile brown fronds remain upright through the winter spreading their spores when warm weather returns.

To eat or not to eat

Spring is when ferns' fronds emerge from the ground unrolling in a manner that reminds one of the head of a violin. Some folks like to collect and eat these “fiddleheads,” particularly those of ostrich fern.

Not all fiddleheads are edible. Bracken fern fiddleheads are toxic, for example. Of course, it varies with how they are prepared and so on. The edibility of ferns raises an interesting question. How come deer and other herbivores are not regularly dining on ferns?

For some of you, keeping rabbits and deer from eating your gardens and landscaping is an ongoing challenge. If you've planted ferns, I bet they remain intact. I may be going out on a limb or, should I say, frond here, but ferns must not taste good.

How did they come by this protective toxicity? Well, the fern fossil record goes back to the Middle Devonian Period, roughly 290 million years ago. Realizing that new fossils might change the timeline, it appears the earliest dinosaurs were tromping around 230 million years ago. I am imagining the herbivorous variety of these titans nibbling on giant ferns and thinking, “Boy, this isn't very tasty.”

Of course, we can't know what dinosaurs were thinking, but somehow ferns have avoided heavy predation through the eons. For instance, our old (and I do mean old) friend sensitive fern dates back 60 million years. This fern's tissues contain numerous toxic chemicals that provide excellent defenses against both invertebrate and vertebrate herbivore. Hungry deer rarely give this fern a second look. Maybe the deer are doing the ferns a favor by eating the competition.

Speaking of which, spring is not only the time to look for fiddleheads, it is also the season to spot young deer. I know I'll take my camera out and try that time-lapse thing with a fern while looking for the deer. With any luck, I might find a fawn under a frond by the pond.

Too much? OK, I'll stop now.

Mark Spreyer is executive director of Stillman Nature Center in Barrington. Email him at stillmangho@gmail.com.