Wearing o’ the Green; an Emerald Isle of Ferns in Our Southern Mountains
by Judy Lundquist

Delicate ferns, growing in shady, moist spots in the southeastern mountains, are deceptively tough customers. Some of them thrive even in deserts and the arctic. They are older than the flowering plants, and still quite diverse, with more than 12,000 species worldwide. With its varied elevations and habitats, the Great Smoky Mountains National Park harbors some 64 species of ferns. Although trees may be the kings of green in the southeastern mountains, ferns are a staple of that color—some of them year round.

Ferns are plants that have leaves but no flowers or seeds. Like the seed plants such as pines and flowering plants, ferns are vascular plants. Vascular plants conduct water, minerals and food via specialized tissues, sometimes in the form of branching veins, in roots, stems and leaves. Vascular tissues enable plants to grow large, and some of the ferns do. Around the southern Appalachians, ferns can grow as tall as six feet, but most of them are much smaller.

What really sets ferns apart from the seed plants is their system of reproduction by means of spores. Like seeds, spores can store nutrients for future plants and may become dormant in dry conditions. That’s where the reproductive resemblance ends. Flowering plants blatantly flaunt their sexual organs within the flowers. Otherwise, their go-between pollinators—animals or wind—could not bring eggs and sperm together for fertilization. That fertilization results in a complete plant embryo sheltered within a seed. Ferns are much more modest. A fern spore quietly settles down and develops a tiny, flat, ground-hugging complete plant—one that has no resemblance to its parent. This little green “skirt” discreetly hides the sexual activity of the fern. On the underside grow the organs that produce eggs or sperm. The sperm travel to the eggs of a different plant by swimming in a thin layer of water. With fertilization accomplished, the resulting embryo develops into a new fern plant. The young fern’s fronds are coiled into tight, spiral fiddleheads that slowly grow and unwind into mature fronds.

For centuries, people had no idea how ferns reproduced. The ferns’ natural modesty, plus sometimes-overactive human imaginations, added up to some peculiar ideas. The thinking went something like this: being plants, ferns must have seeds, so the seeds must be invisible. People weren’t too far off—fine and dust-like, the spores are near-to-microscopic. But then things got a little out of hand. Stories were told of people wandering through the woods, where the fern “seed” fell by chance into their shoes. Immediately invisible, they ran home to startle their families with their disembodied voices. Shakespeare’s Henry IV features a thief trying to persuade another to join him in crime: “We steal as in a castle, cocksure; we have the receipt of fern-seed, we walk invisible.” The skeptical reply: “Nay, by my faith, I think you are more beholding to the night than to fern-seed for your walking invisible.”

In those times, looking for fern seeds, perhaps for nefarious purposes, had many prescriptions. The seeker had to perform convoluted rituals to succeed—after all, finding the invisible was not easy. Although it’s still not easy, magnification, not magic, is the key to finding fern spores. Look on the underside of the fronds for dark round or oblong dots. Clusters called “sori” contain the spore sacs. The sacs, called “sporangia” produce the spores. Each species has its own pattern of sori. The spores themselves are protected within the sporangia until they are ready to make their mark in the world. The sporangia then open, often with sudden force, and the spores escape. The next generation is essentially pitched to the wind, so ferns make a lot of spores.

The need for water to accomplish fertilization explains the ferns’ association with rain, shade and dampness. Those living in arid places still need the occasional rain or mist for the genetic mixing of egg and sperm. However, many ferns hedge their reproductive bets. Cells on the fronds or rhizomes (underground stems) form new plants that root and develop into independent plants. One fern makes such a habit of this that it is known as the Walking Fern. New plants grow at the tips of the fronds, colonizing wet rocky places step by green step. Walk along trails at low to mid-elevations in the Smokies, and you can see the small Walking Fern here and there, green even in winter..

Another way of reproducing, especially in arid spots, is to make a kind of spore that skips the sex altogether. The spores grow into independent plants on their own. The Purple Cliffbrake inhabits the rockwork of bridges and walls in the Smokies because it likes the lime in the mortar. A vertical stone wall can be a pretty dry place. The Cliffbrakes’s spores germinate and develop into a complete plant with roots, stems and leaves. Although ferns like the Cliffbrake and Walking Fern reproduce asexually, the “offspring” are genetically identical to their parents. Apparently there’s more than one way to carry on the family tradition.

That tall, green frondy thing on the forest floor may be obvious, but ferns also come in unusual forms that look quite un-fernlike, even bizarre. The Climbing Fern spreads on the ground until it comes to a more vertical landscape. The central rib of its frond wraps around the supporting plant, and it’s off and climbing. It’s easy to miss, since at first glance it looks like any other climbing vine. Keep an eye out while hiking at lower elevations. It seems to like a bit of sun and can sometimes be found at open spots along trails and roadsides.

The Rattlesnake Fern doesn’t much resemble its more conventional cousins, either. In spring it sends up a vertical stalk that carries prominent sporangia on a series of lateral branches. This assemblage looks a little like green berries. Look for it in woods at middle and lower elevations. The Rattlesnake Fern is supposedly associated with ginseng and can be used to find that valuable plant—another bit of folklore.

Most un-fernlike, the Adder’s Tongue grows as a small, spoon-shaped frond. Close to the ground, inconspicuous, this unassuming little fern looks like any other small plant just starting life as a solitary leaf. In the spring it becomes a bit more obvious when the fertile part of its frond reaches up as a single spike bearing two rows of sporangia. As for the reptilian names for these ferns, a fancied association between some ferns and snakes goes back a long way. Adder’s Tongue is a very old name for this plant. In ancient times it was used in ointments for snakebite.

People have traditionally thought that the plants known as fern “allies”—club mosses, spike mosses and horsetails—are closely related to ferns, probably because they have basically the same life cycle. It has taken DNA analysis to reveal that some of them are not even closely related to each other, much less to ferns. Club mosses, judging by their form and fossils, are quite different from ferns and seed plants. Their DNA bears this out—ferns and seed plants are actually more closely related to each other than either is to club mosses. The club mosses are diminutive, ground-hugging, shiny green pine mimics, sometimes complete with “cones,” the strobuli that carry the sporangia. Most southeastern mountain habitats have some kind of clubmoss. In some places, they form abundant ground covers. Spike mosses do not have true roots. The stems are usually branched, with small simple leaves that are arranged in four rows, with two rows having long leaves, and two with small leaves.

One of these unassuming little club mosses has a trick up its sleeve. Its spores can be explosive. Though they contain some oil, the spores are not actually particularly flammable—a lighted match touched to a pile of them goes out. However, if enough spores are dispersed into an airborne dust, any spark will produce a spectacular fireball. Early on, they were used in fireworks and flash photography. Lycopodium powder, named for the genus of this club moss, can still be purchased, complete with a Material Safety Data Sheet. Thankfully it is no longer necessary for flash photography, but science teachers still use it in their labs to wake nodding students.

The fern allies most closely related to ferns, but looking perhaps the least like them, are the horsetails. Despite their jointed, ribbed stems, with rings of branches or scale-like leaves at the joints, DNA studies show that horsetails are ferns. Fertile stems bear a cone containing the sporangia at the top. All of the stems incorporate silica. These sharp mineral crystals discourage browsing by animals, but make the plant an effective pot scrubber or sandpaper. It is still used to sand reeds for musical instruments. One species, the deciduous field horsetail, looks a bit like small green bottle brushes. The jointed stems identify it as a horsetail. Its larger, more robust evergreen cousin, the scouring rush, can be found even in urban areas. It is sometimes grown as an exotic-looking garden plant, but beware—it loves water and has a talent for finding your plumbing. To see horsetails in the wild, try open wet areas like marshes and roadside ditches at low elevations.

Beyond enjoying the obvious beauty of ferns and club mosses, learning to identify more of them is a satisfying excuse to hit the trail. If you want to explore these wonderful plants more carefully, take a hand lens and guidebook along.. The names alone are fun: Mountain Spleenwort, Hairy Lip, Silvery Glade, Sensitive, Cinnamon, Royal, Resurrection. They welcome us to the woods and fields with 1,000 shades of green, but are rewarding in more than just the visual sense. Want to know how green smells? Sniff a Hay-scented fern. If you can’t get to the actual Emerald Isle anytime soon, the ferns of the southern Appalachian highlands will provide a lovely substitute.

Thanks to Tennessee Valley Authority botanist Patricia Cox for her helpful comments.