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Common Name: Evergreen Wood Fern
Scientific Name: Dryopteris intermedia

(Information for this species page was gathered in part by Ms. Lindzy Hall for Biology 220W at Penn State New Kensington in Spring 2013)

Evergreen wood fernEvergreen wood fern (Dryopteris intermedia) is a common, perennial fern that is frequently found in the understory vegetation of hardwood forests in the northeast United States and eastern Canada. It is also occasionally found in the hardwood forests of Europe. It is a plant of moist, shady areas (especially woods, ravines, and the marginal edges of swamps). It is more abundant in “primary” (uncut) forests than in secondary (successional) forests, but grows well and reproduces robustly in each. Some studies have indicated that this fern favors tree holes (the excavations formed by a wind-thrown tree) but other studies have emphasized the generalized nature of its distribution. As its name implies, this fern stays green all year round. It is thought that maintaining the chlorophyll in its fronds (and, thus, its green color) through the winter enables the plant to begin photosynthesis earlier in the spring giving it an energetic edge over its forest floor competitors. (Image credit: D. Sillman)

Out on our campus Nature Trail we have found that evergreen wood fern is especially abundant up in the ridge top hardwood forest while down in the wetter ravine Christmas fern is the more abundant “evergreen” fern species. These observations may be indicative of Christmas fern’s higher demand for moisture and/or evergreen wood fern’s very broad tolerance of habitat conditions.

Evergreen wood fern grows to heights of one and a half to three feet. Its fronds can be up to forty inches long. The leaflets on the fronds are lobed and toothed, and the teeth have bristle-like tips. The stem is grooved with brown scales on the base and small, hairs on its upper section. It grows and spreads both via sexual reproduction and via vegetative propagation from its extensive, underground rhizome.

Life Cycle
The sexual life cycle of the evergreen wood fern illustrates the plant reproductive pattern called “alternation of generations.” There are two distinct, multicellular life stages in this cycle. The “sporophyte” is the conspicuous form of the plant. This stage is diploid (i.e. has two, complete sets of chromosomes) and is the green fern that we see growing in the woods. The reproductive task that the sporophyte accomplishes is the formation of haploid (having just one complete set of chromosomes) spores in specialized structures called sporangia. These spores are formed via reduction division (“meiosis”) and represent the dispersal life form for the fern.

Sori on the underside of a frond of everygreen wood fernThe tiny, haploid spores are found in dark structures called sori that are located on the undersides of the leaflets on fertile fronds. The spores are blown or washed away from the parental fern and may travel some distance before they eventually find their way into moist soil. Here the spore will begin to mature and grow (via mitosis) into a haploid, multicellular life stage called the gametophyte. The gametophyte is small and inconspicuous. It grows in the soil and often is sustained by mutualistic interactions with soil fungi. In the gametophyte are the specific structures that produce the gametes (“reproductive cells”) for the fern. It is interesting that even though ferns only produce one kind of spore (they are “homosporous”) the gametophyte that arises from that spore can have three different combinations of reproductive structures. Most of the gametophytes (60 to 70%) will make only female gametes (“ova”), a much smaller percentage (17 to 27%) of the gametophytes will make only male gametes (“sperm”), while an even smaller percentage of the gametophytes (13%) will have the structures that can make both ova and sperm. Production of certain plant hormones determines the reproductive potentials and fates of the gametophytes, and it is suggested that environmental conditions, in turn, control the production of those plant hormones. (Image credit: D. Sillman)

Sperm must swim within environmental water films in order to reach and fertilize the ova. For fern reproduction, then, it is essential that the plant (or at least the gametophytes of the plant) be in an environment that is extremely moist. Fertilization of the ova occurs in the female gametophyte and results in a new, diploid sporophyte which begins to grow via mitosis.

New sporophytes, either generated by ova fertilization or vegetatively formed from the underground rhizome, push their way out of the soil in the early spring as tightly coiled structures of stems and fronds called “fiddleheads.” These fiddleheads uncoil and grow into the large above ground plant of the fern. As the fern grows its cells will synthesize the rich array of secondary chemicals that render the fern nearly immune from herbivorous predation. The fiddlehead contains, then, only very low levels of these secondary chemicals, and, with proper preparation (boiling and rinsing), is safe for human consumption!
Some animals (like white tailed deer and rabbits) also consume these fiddleheads, but they ingest small quantities of the fern toxins in the process. These toxins may have a deleterious impact on the long-term health of these foraging animals.

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This page was last updated on August 18, 2014  

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