Ferns of the Adirondacks:
Christmas Fern (Polystichum acrostichoides)
Christmas Ferns (Polystichum acrostichoides) are evergreen ferns with dark green, leathery fronds. They are found in the Adirondack Mountains of upstate New York, most commonly in hardwood forests under Sugar Maples.
The Christmas Fern is a member of the genus Polystichum (Holly Ferns). The Christmas Fern is one of two species in this genus that occurs in the Adirondacks. The other – Braun's Holly Fern (Polystichum braunii) – is much less common in our region.
- The genus name is derived from the Greek "polys," meaning "many", and "stichos," meaning "row". This is a reference to the rows of soriSorus: A cluster of spore-producing receptacles (sporangia), usually borne on the underside or margins of the pinnae or pinnules. (plural = sori) (spore-producing structures) that are common to this genus.
- The species name (acrostichoides) is a reference to a tropical genus of ferns with a similar arrangement of spore-producing structures.
The nonscientific name (Christmas Fern) refers to the fact that the fern's evergreen fronds were used for decoration during the Christmas holidays.
Identification of Christmas Ferns
Christmas Ferns are medium-sized, evergreen ferns that grow 1½–2½ feet high in asymmetric clumps. The fronds arise from a central rhizome
Rhizome: The modified subterranean stem of a plant that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks and rootstocks.. Christmas Ferns can form small, loose colonies or can occur individually.
The Christmas Fern's rachis
Rachis: The stalk within the blade (the expanded, leafy part of the frond). (central stalk) is light green to medium green and covered with white to light brown scales. The stipe
Stipe: The stalk below the blade (the expanded, leafy part of the frond). (the part of the stalk arising immediately from the root stock) is about ¼ to ½ of the length of the overall frond and is covered with coarse, brown scales.
The Christmas Fern's fiddleheadsFiddlehead: The unfurling young frond of true ferns, which loosely resembles the ornate, curled end of a fiddle. (Synonym=crosier) (the unfurling young frond) appear in early spring among the recumbent green fronds of the prior year. The fiddleheads are light green and covered with silvery, white scales.
The dark green frondsFrond: The whole leaf of a fern. It includes the blade (the expanded leafy part of the frond) and the stipe (the stalk below the blade). of Christmas Fern are 12 to 32 inches long and 1½ to five inches wide. They are rather leathery in texture, with sparse hairs on the underside.
Each frond has 20 - 35 pairs of pinnae
Pinna: A primary division of the blade (plural: pinnae). (leaflets). The two lowest leaflets are nearly opposite
Opposite Leaves: Leaves occurring in pairs at a node, with one leaf on either side of the stem., while the rest are arranged alternately
Alternate: An arrangement of leaves (or buds) on a stem (or twig) in which the leaves emerge from the stem one at a time. This often makes the leaves appear to alternate on the stem. along the rachis. Each leaflet is about 1½ inches long. Leaflets are oblong with a distinctive lobe at the base, resembling the toe of a Christmas stocking. Leaflets marginsThe structure of the leaf's edge. are usually finely serrated and bristle tipped, with teeth curving upward. However, there are variable forms, with some specimens displaying leaflets that are twisted or deeply cut.
Christmas Ferns are dimorphicFrond dimorphism: Refers to a difference in ferns between the fertile and sterile fronds., meaning that the fertile fronds and sterile fronds are somewhat different.
- Fertile (spore-bearing) frondsFertile frond: A frond with sporangia (spore cases). are taller and more erect. Only the upper portion of the fertile frond bear spores. The upper leaflets of fertile fronds are much smaller that the sterile leaflets lower on the frond. When mature, the lower surface of these fertile leaflets are completely covered by rows of sori (spore-bearing structures). The sori are oblong and gradually expand to cover the entire surface, becoming covered with a circular indusiumIndusium: A thin layer of cells which usually covers and protects the sorus. (plural = indusia) and turning dark brown to blackish. The sori release their spores to the wind in the summer or early fall. Only the nonfertile portions of fertile fronds remain evergreen.
- Sterile frondsSterile frond: A frond without sporangia (spore cases). are shorter and more arching than fertile fronds. They remain evergreen over the winter, but are usually flattened by snow.
Uses of Christmas Ferns
Christmas Ferns were used by early New England settlers as a Christmas decoration. Although Christmas Ferns do not appear to have any edible uses, Native American groups used it for medicinal purposes. The Cherokee, for instance, used Christmas Fern externally to treat rheumatism, rubbing a decoction of the root on the affected area. An infusion of the plant was also taken internally for rheumatism. The Cherokee used Christmas Fern to treat stomachache, pneumonia, toothache, and chills. The Iroquois also used the plant to treat a wide range of medical problems, including rheumatism, consumption, convulsions, and fevers.
Wildlife Value of Christmas Ferns
Christmas Ferns appear to have limited value for wildlife. In general, ferns are not a major food source for either mammals or birds. The small size of fern spores eliminates them from significance as a menu item. Many ferns are deciduous and so cannot provide a food source after the fronds have died back with the coming of cold weather.
Because the Christmas Fern is evergreen, it is of slightly more importance. During harsh winters when little else is available, White-tailed Deer may consume the evergreen fronds. The young fronds may be eaten in the spring by Wild Turkey and Spruce Grouse. Christmas Fern is reportedly a significant part of Ruffed Grouse diets during fall and winter. A few bird species (such as Ovenbirds and Veery) are reported to use the overwintered fronds of Christmas Fern as a nest site in the spring. The Christmas Fern is a larval host for the Serpentine Webworm.
Distribution of Christmas Ferns
The Christmas Fern is one of the most common ferns in the eastern United States. These ferns are found from Nova Scotia to southern Ontario, south to Florida and eastern Texas. This fern is listed as threatened in Minnesota and as a plant of special concern in Wisconsin.
The Christmas Fern is found throughout New York State, where it is among the many ferns listed as exploitably vulnerable. Vouchered plant specimens have been registered for nearly all counties in the state, including all counties within the Adirondack Park Blue Line.
This pattern is consistent with the map of iNaturalist observations of Christmas Ferns in New York State. The insights gleaned through iNaturalist should, of course, be tempered with an awareness that the data reflect the number of observers willing to submit photos and how easily recognized a particular species is, rather than the actual abundance of the species. With this caveat in mind, it appears that Christmas Ferns are fairly common throughout much of the state. As of early December 2020, there were 1,700 research-grade observations of Christmas Ferns in the state. This compares with nearly 15,000 observations of all species of ferns, suggesting that this species is one of the more common (and more easily recognized) ferns.
The Christmas Fern appears somewhat less widespread in the Adirondack Mountains. The lower density of observations reflects partly the lower population density in our region and partly the lengthy period of heavy snow cover obscuring everything growing on the forest floor. As of early December 2020, there were 71 research-grade observations of Christmas Ferns within the Adirondack Park Blue Line, compared to more commonly-reported species, such as Intermediate Wood Fern (138 observations) and Sensitive Fern (124 observations).
Habitat of Christmas Ferns
The Christmas Fern is classified as a Facultative Upland plant (FAC), meaning that it usually occur in non-wetlands, but may occur in wetlands. In terms of site requirements, this fern is fairly shade tolerant, but can tolerate sun if the soil is moist. It is found in a variety of shaded habitats, including woodlands, stream banks, and rocky slopes. In New York State, Christmas Fern is most commonly found in hardwood forests with richer soils. In the more northern parts of the state, it becomes less common and more restricted to rich and rocky soils.
In the Adirondack Mountains, Christmas Ferns are found in several ecological communities, including:
One of the likeliest places to find Christmas Ferns is the beech-maple mesic forest. This is a northern hardwood forest where the two codominant species are Sugar Maple and American Beech. These forests are generally found in areas with moist, well-drained, slightly acidic soils.
- Other deciduous trees found here include Red Maple and Yellow Birch. A few Eastern Hemlocks and Red Spruce trees may also be found.
- In the understory of the Beech-Maple Mesic forest, look for characteristic shrubs/small trees such as Hobblebush, Striped Maple, Maple-leaved Viburnum, and Alternate-leaved Dogwood.
- Characteristic wildflowers include Canada Mayflower, Starflower, Common Wood Sorrel, Partridgeberry, Foamflower, Whorled Wood Aster, Indian Cucumber-root, Wild Sarsaparilla, Jack-in-the-Pulpit, and Sessile-leaved Bellwort, as well as spring ephemerals such as Trout Lily.
- Other ferns that flourish in this habitat together with Christmas Ferns include Marginal Wood Fern, Intermediate Wood Fern, and Spinulose Wood Fern.
Among the trails covered here, look for Christmas Ferns growing under Sugar Maples on the Sugar Maple Trail at Heaven Hill and the Rocky Knob Trail at Henry's Woods.
List of Adirondack Ferns
References
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