Nature made ferns for pure leaves to see what she could do in that line. Henry David Thoreau
Ferns surpass other plants in the varied and graceful designs of their leaves. Like other green plants, ferns capture sunlight and turn it into energy to grow and reproduce. But, unlike many other kinds of plants, ferns do not produce flowers or seeds. Instead, they reproduce by means of spores, particles so small that they float in the air like so many specks of dust. Carried by wind and storm, the spores of ferns have reached every part of the globe; nearly every habitat on the earth, from tropical jungle to icy mountaintop, is home to some ferns.
Although there are only 10,000 species of ferns in the world, compared to 300,000 species of flowering plants, many ferns have worldwide distribution. The lovely bracken fern of our northeastern forests is also found in Britain and Europe, Asia, New Zealand, and Australia. The tropics have not only the largest number of ferns, but also the largest in size. Tree ferns can reach heights of forty feet. Even in New England, 100 different species of ferns are found, and it’s not hard to find a dozen species living within a short distance of each other.
The arrival of spring is heralded by the appearance of fuzzy spirals poking up through the soil and leaf litter. As these little curls grow taller and begin to unfurl, they resemble the scrolled neck of a violin, giving them their common name of fiddleheads. Each fiddlehead is a single coiled leaf, or frond, of a fern plant, its delicate growing tip protected inside the coil. As the stem unfurls, the lower leaflets uncoil and begin their work, providing energy for the frond to grow longer and fill out until the full new frond is complete. All fern leaves begin as fiddleheads, and some kinds of fiddleheads can be cooked and eaten for a tasty spring dish.
The leaves of most ferns follow a basic body plan with narrow stem and broad, triangular blade. The lacey nature of fern fronds comes from divisions of the blade into leaflets and subleaflets. Some ferns, like the walking fern and Hart’s tongue fern, have a solid or “entire” blade, with no divisions or lobes.
In some ferns the blade is divided horizontally into many smaller leaflets, extending at right angles from the stem. These are called once-cut ferns. The Christmas fern, so-called because its dark green foliage keeps its color through the winter, is a once-cut fern, as is the sensitive fern, which is found in fields and damp places with lots of sunlight. Another once-cut fern is common polypody, which grows on limestone rocks and cliffs.
Ferns in which each leaflet is further divided into subleaflets are called twice-cut ferns. The ostrich fern, named for its very tall, plume-like fronds, is twice-cut, as is the cinnamon fern, named for the cinnamon-colored fluff that cloaks its stems, and the interrupted fern, common along roadsides.
The laciest of all the ferns are those with thrice-cut leaves. In these, every subleaflet is further subdivided into tiny lobes. The hayscented fern, a pale-green lacey thrice-cut fern, lends its wonderful fragrance to upland meadows and sunny openings in the woods. The graceful vase-like lady fern is another thrice-cut fern and grows in circular clumps. It is more common in shady glens than open fields and can be recognized by the dark scales on its light green stem.
Looking at the overall shape of the frond, most ferns can be grouped into one of three basic shapes. A frond can be triangular, narrowest at the tip and broadest where stem meets blade. Another common shape is semi-tapered. In these ferns, the leaf tapers very slightly back towards the stem. A third common form is a leaf that is tapered at both the tip and where it meets the stem so that it is broadest somewhere in the middle of the blade.
Besides the fronds, a fern plant consists of a rootstock, akin to a trunk, from which the leaves grow upward and the roots down. In most northern ferns, the rootstock grows beneath the soil so that the leaves appear to originate at or near ground level. In tropical tree ferns, the rootstock grows above ground and can be very tall, supporting a crown of twelve-foot long fronds high above the ground. Ferns do not grow taproots but have thin, wiry, branching roots that spread out through the soil in search of nutrients and moisture. Some ferns are vase-like, growing from a central rootstock and forming a circular grouping of leaves, each plant distinct from its neighbors. Other ferns have rhizomes, root-like stems that creep along just under the soil, which send up fronds at intervals so that a bed of these ferns appears to be made up of many individuals.
Another clue that is most useful in fern identification comes from the design and location of the fruitdots on the undersides of fronds. The name fruitdots is a misnomer, for ferns produce neither flowers nor fruits. In fact, the botanical name for these structures is sori and they contain the spore cases and spores by which ferns reproduce. Sori are found on the undersides of the fronds in some ferns like Christmas ferns and polypody, or under the rolled-up edges of leaflets in bracken and maidenhair fern. On the interrupted fern, all the sori are carried on several leaflets midway up the frond, giving this fern its “interrupted” appearance. In some ferns, spores are carried on separate specialized structures called fertile fronds. The ostrich fern and sensitive fern have separate hard, brown spore-bearing fronds that remain standing after the leaves have died back, scattering their spores throughout the winter. Cinnamon ferns have a separate fertile frond that produces spores in early spring and then dies back, making it hard to find by late summer.
When the spores are mature, the sori rupture and the spores are released, to be carried by wind to their future destinations. Those that land in suitable places take root and produce a tiny heart-shaped leaf, no more than a half an inch long, called a prothallus. This is an intermediate stage in the life cycle of the fern. On the underside of the prothallus, two types of structures form. One kind contains unfertilized eggs and the others contain sperm. The sperm cells need moisture, from rain or dewdrops, to find their way to neighboring prothalli where they may fertilize an egg. The fertilized egg develops into a new fern plant, sending a root down into the soil and a shoot upwards to become the first frond of a new fern plant. Many ferns also reproduce by sending up shoots from spreading rhizomes, though these will be clones of the parent.
Though all ferns follow a similar pattern of blade and stem, the designs of their leaves are like so many variations on a theme. From delicate miniatures to leafy giants, ferns add beauty and variety to our landscape.
Suggested Reading
Westin, Doug and Sue Westin. Common Ferns of Vermont, edited by Ginger Anderson, Vermont Agency of Natural Resources, 1995.
Hallowell, Barbara and Anne Hallowell (Illustrator). Fern Finder: A Guide to Native Ferns of Central and Northeastern United States and Eastern Canada, Nature Study Guide Publishers, 2001.
Cullina, William. Native Ferns, Moss, and Grasses: From Emerald Carpet to Amber Wave, Serene and Sensuous Plants for the Garden, Houghton, Mifflin, Harcourt, 2008.
Cobb, Boughton, Cheryl Lowe, and Elizabeth Farnsworth. Peterson Guide to Ferns of Northeastern and Central North America, Houghton, Mifflin, Harcourt, 2005.
Whittingham, Sue. Fern Fever: The Study of Pteridomania, Francis Lincoln Press, 2011.
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