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May 09 2012

A fair fern mystery

By Dr. John Nelson

What ever could this fern be? (Photo by John Nelson)

Botanists tend to be rather easy-going people. They enjoy being outdoors on field trips and seeing interesting plants, and some botanists are known for an occasional and perhaps unusual sense of humor. Over the years, my own long-suffering students have been subjected to a wide variety of brilliant anecdotes and excellent puns. (Well, that’s the way I think about them.) One of my little stories involves ferns: whenever we come up to a patch of them growing in the woods, I usually end up remarking that we must be in “Fern land,” and that maybe we are near Helsinki. (I’ve got plenty more similarly excellent jokes, but maybe I’ll share them with you at a later time.)

But seriously, folks. Ferns represent an extremely ancient plant lineage, easily dating back to the early Carboniferous period some 345 million years ago and well before the first dinosaurs. They and their relatives were instrumental in the development of vast deposits of coal as they died and decayed, and their legacy as a source of fossil fuels makes them extremely important – at least as far as human economy goes. From these deposits, fossilized ferns are commonly encountered. Modern ferns are indeed vascular plants, meaning that their roots, stems, and leaves contain various tissues that transport water and dissolved substances. Ferns do not produce flowers, however, nor do they produce seeds in the way that flowering plants do. Rather, ferns and their relatives reproduce by spreading tiny spores. The spores commonly originate in specialized structures, called sporangia, on the lower sides of the fronds. Depending on the particular kind of fern, these sporangia will be arranged in a rather characteristic pattern. The pattern appears on the divisions of the frond often as small, roughened dots, each one of which is called a “sorus,” or “sori” when plural. Our Mystery fern, however, is somewhat unusual in having its sporangia not consigned to sori as in many other ferns, but rather at the margins of the frond’s ultimate divisions where they are hidden away and protected by a thin, overlapping margin of leaf tissue.

This is a common fern species in deciduous forests all over the eastern United States, from New England to northern Florida, and as far west as Oklahoma. In the southeast you will find it in the piedmont and mountain counties, generally away from the coast. It likes to grow in damp shady places, but it can be found in open sites, as well. The plants come up from a horizontal stem that clings to the soil or to rocks, and each frond has a smooth, shiny, nearly black stalk. The frond is prominently divided into many divisions, and the effect is something like a fan. The divisions of the frond are quite delicate, affording a lovely shimmering effect in the slightest breezes, such as those near waterfalls.

So there we are. “Sori” for all the fern jokes.

John Nelson is the curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196.

[Answer: “Maidenhair fern,” Adiantum pedatum]

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