Northern Minnesota phenology for May 2014: Ferns

By: John Latimer

The shady forest floor will be perforated by dozens of species of ferns throughout the month of May. Nearly every one of them uncurls like the tongue of a butterfly. Most of these emerging ferns fall under the rubric of fiddleheads. They look like the head of a fiddle and are often harvested in the spring as a green vegetable. While there are about five- dozen species of ferns found in Minnesota we shall consider three of the most common here.

Fern Underside - Trabuco Canyon, CA. Flickr CC-licensed photo by M. Dolly.
Fern Underside – Trabuco Canyon, CA. Flickr CC-licensed photo by M. Dolly.

Ferns differ from flowering plants by the way they reproduce. Flowering plants do just that; flower. In the flowers, male and female parts are present. And through often convoluted schemes the two are united to produce seeds that contain the necessary genetic information to create a new plant. Ferns reproduce through spores a more primitive technique.

Spores may be created on the fern itself or the fern may create a fertile stem separate from the sterile and familiar frond. Either way the fertile structures where the spores are developed are called sporangiophores. The spores are dispersed by the wind and fall to earth where they grow a tiny plant called the prothallium. It is here that the male and female parts arise and the union of the two results in a new fern.

One of the first of the ferns to emerge is the interrupted fern. The fiddlehead is cloaked in a light tan, furry coat. As it grows the hairs fall away until at full development any remaining hairs are very nearly microscopic. This is perhaps the easiest fern to identify because of the tan coat of hairs at emergence and the “interruption” of the normal growth of the fronds by the spore producing structures. These withered looking branches occur right in the middle of the fronds interrupting the normal development of the fern. The sporangiophores emerge a dark green and become a deep brown as they mature.

As fiddleheads go this is not the one you want to eat. Most ferns contain some cancer causing chemicals, some more than others but this is not the real danger. Interrupted ferns simply do not taste good. They are bitter and they will give you diarrhea, two good reasons to avoid the fiddleheads wrapped in furry tan coats.

Matteucia struthiopteris - Ostrich fern. Flickr CC-licensed photo by Tatiana Bulyonkova.
Matteucia struthiopteris – Ostrich fern. Flickr CC-licensed photo by Tatiana Bulyonkova.

The ostrich ferns are the next ones to emerge. The average date here in southern Itasca County is May 7th. These ferns are a deep green as they unfurl. Perhaps the easiest way to find them is to look for their Fertile stems from the previous year. In this fern the sporangiophores are a separate structure. As the name implies these fertile stems look like ostrich feathers. They persist through the winter and are easy to locate after snow melt. They are dark brown and stand about a foot tall. The spores are carried inside what looks like segmented worms.

These magnificent ferns arise from last year’s root cluster and recreate the almost vase-like structure of the mature plant. Around here they grow to almost 4 feet in height. To support such large fronds the stems are deeply “U” shaped. This feature is diagnostic for no other fern has a cross section quite like this.

Ostrich ferns are the ones referred to when people talk about gathering fiddleheads. These are the tastiest of the lot and are deemed to be the safest to eat. That is not to say they are perfectly safe. They need to be boiled for several minutes and the water should be discarded. There are several cases in the literature of people getting sick when the fiddleheads were merely fried with butter for a few minutes. Stomach upset, diarrhea and some vomiting were the result.

Bracken ferns are the next ones to arise. They are furled just like the others but they quickly unroll to reveal their three branches. Bracken never grows in clumps, they may grow quite close together but there is never a pattern to them.  These ubiquitous ferns can be found in almost every environment in the state with the exception of the dry prairies. They will grow in shade or sun, on dry or wet ground, and in humus or well-drained sandy soils. Because they prefer dry open sites with light soils they are far and away the most common ferns encountered in the state. They are edible but because they contain small quantities of carcinogens they should be eaten sparingly. Since they are only available for a short period in the spring this should not be an over-riding concern.

The beauty of ferns is easy to see and when fiddleheads appear on the plate they are a gorgeous green and curled into a lovely shape. I like to enjoy a serving or two each year as a way of celebrating the arrival of the season. Even if you choose not to partake, they are wonderful to observe in the wilds and a sure sign of spring.

From the phenology notebook:

 May 6, 2011    The raven fledglings are now nearly the size of crows, and anxious to begin flying. The trembling aspens appear green as the female catkins approach maturity. The green of the catkins is just slightly darker than the green of the new leaves and precedes their emergence by three or four days. Morel mushrooms are starting to emerge and as you are searching for them keep an eye out for the fiddleheads of the interrupted ferns. Leatherwood leaves are just starting to emerge. This usually marks the end of the flowers.

 May 14, 2001    The ovenbirds have returned. I heard one singing this morning. They must migrate at night since it is always in the morning when I hear them for the first time. Other songs heard today were the American toad and the gray tree frog. This is the first day of the return of the female ruby throated hummingbirds. The first males were seen on the ninth. Red maples are starting to break leaf buds. The ostrich ferns are beginning to unfurl. The leatherwood shrubs are nearing their last flowers.

 May 31, 2002      Jack-in-the-pulpit are starting to flower and are accompanied by starflowers, wild sarsaparilla, three leaved soloman’s seal, and water arum. The interrupted ferns are beginning to develop their spore producing structures, and bracken ferns have begun to separate into their familiar three branches.  A thirteen lined ground squirrel darts across the driveway in front of me and the first Canada tiger swallowtail butterflies have emerged from their chrysalis. These large yellow butterflies emerge within a few days of the arrival of the monarch butterflies. This is interesting because the monarchs migrate and the swallowtails emerge from chrysalis, and yet their timing is remarkably similar.

John Latimer is well known throughout northern Minnesota for his phenology work.  John appears weekly on KAXE radio in Grand Rapids, and audio and twitter archives are available here. We hope his work will be a frequent feature on MyMinnesotaWoods.  This article also appeared in the Duluth Senior Journal.  It is printed with the author’s permission.

The University of Minnesota Extension Forestry team.

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  1. Are ostrich ferns common across the Iron Range/NE MN? I would like to harvest the fiddleheads.