Graceful ferns a fiddling
“Marvel for a moment at the fern fiddlehead. It stands like a watch spring coiled and ready to unwind … What many do not realize, however, is that the fiddlehead has some unusual mathematical properties. It represents one of two kinds of spirals commonly found in nature, and this spiral results from a particular kind of growth.”
— Robin C. Moran, A Natural History of Ferns (2004)
Ferns lend an always-graceful sometimes-ethereal touch to our mountain landscapes year round. Even in winter there are evergreen species that provide welcome splotches of greenery.
The fiddleheads of ferns are emerging right now from the leaf litter. Even those not especially interested in wild plants have heard of “fiddlehead ferns” and often think they’re a specific kind of fern.
But fiddleheads aren’t a species of fern. They’re a growth strategy. All ferns — to a greater or lesser extent — display the characteristic fiddlehead shape as they unfurl from their underground rhizomes.
The “fern leaf” (frond) differs from the “true leaf” of the flowering plants in its manner of expanding from the bud. The frond unrolls from its tip rather than expanding from a folded condition.
This unfurling strategy helps the immature frond (crozier) make its way upward through the soil and leaf litter. It also protects the developing leaflets (pinna and pinnules) that will comprise the leafy portion of the mature frond.
In addition to being highly functional, the emerging fiddleheads of some fern species are quite beautiful. Those of cinnamon fern (Osmundia cinnamomea) are a pale lime green and can stand a two feet or more high before unfurling. Species in the wood fern genus (Dryopteris) display wooly greenish-brown fiddleheads.
When most people bring up fiddleheads, they do so because they’ve looking for something to eat. They want to know which ones can be harvested for consumption. My answer is that few of the ferns in the southeastern United States are choice edibles. And the one that’s said to be particularly tasty is also thought to be dangerous.
Bracken (Pteridium aquilinum) is distributed worldwide, being commonly found along roadsides and in disturbed areas with poor soil. They display exquisite silvery-gray fiddleheads shaped like an eagle’s claw.
Bracken is reputed to be delicious, but the species contains a number of toxic substances that readily kill livestock and cause stomach cancers in human populations (as in Japan and China) that eat substantial amounts of the plant.
Unfortunately, for us, the North American fern species bearing fiddleheads that are reputed to be both delicious and safe doesn’t grow wild in our region. That’s the ostrich fern (Matteuccia struthiopteris). Its distribution range is circumpolar, extending only as far south as Virginia in eastern North America.
The good news is that Ostrich fern grows just fine when propagated in damp shade in Western North Carolina. Some years ago, my wife, Elizabeth, who is an artist, and Murray Evans (then the fern expert at the University of Tennessee) agreed on a swap.
When back home in his native state of Vermont, Murray dug up 20 ostrich ferns, which were prolific on his farm, and shipped them to Elizabeth in exchange for a painting.
The transplanted ferns are prospering (as ornamentals) in our yard. And like everything else in the universe, ostrich ferns are available from various vendors on the Internet, if you want to give them a try.
Now, we get to the part about the fiddlehead spirals.
According to Robin C. Moran, “The first kind of spiral is the equable spiral, or the spiral of Archimedes ... which can be illustrated by the way a sailor coils a rope upon a ship’s deck. Because the rope is uniform in thickness, each whorl is the same breadth as the one that precedes or follows it.
The second type of spiral — the one found in fiddleheads — is the equiangular. It was first described by the French philosopher and mathematician Rene Descartes in 1638 … Spiraling outward, each whorl is wider than the one preceding it … A fern fiddlehead has this type of spiral because its midrib widens at a constant rate as it spirals toward the base of the stalk.”
Subsequent mathematicians referred to the equiangular spiral as the “spira mirabilis” or wonderful spiral because of its unchanging shape as it grows.” That is, “the larger spirals are just expanded versions of the smaller spirals within.”
These are the patterns that please us when we see them in shells of Nautilus, in the way forget-me-not uncoils as it flowers, in the curvature of a ram’s horn, and in many other spirals that appear in the natural world.