Shape: Christmas Fern is an evergreen fern growing in circular arching clumps.
Fronds: They are dimorphic, that is the fronds are either sterile or fertile. Fronds are pinnate and do not have the pinnae divided into individual pinnules. Fronds have from 20 to 40 pairs of pinnae, the two lowest often point downward away from the blade plane. The lower pinnae appear opposite but from the middle of the frond upward they appear alternate. Sterile fronds and the non-fertile part of fertile fronds remain evergreen over winter, but usually flattened by snow load. The rachis is green and scaly. The stipes are grooved and scaly, with 5 vascular bundles. Stipe length is 1/4 to 1/3 the length of the blade.
Sterile fronds are once pinnate, arching, paler color beneath with hair-like scales. Above they are darker green and scaleless, also shorter and less erect than the fertile fronds.
Fertile fronds have both sterile and fertile pinnae. The upper pinnae are fertile and are much smaller then the sterile pinnae lower on the frond.
Pinnae: On all pinnae an auricle (lobe) at the upper side of the base points upward to the tip of the blade. The margins of sterile pinna have spiny tipped teeth that curve upward. Veins in the pinnae are forked and extend to the margin of the pinnae. Overall, the mature pinnae give the fronds a leathery dark green appearance.
Fertility: Sori are oblong, green initially then tan colored, covered with a circular indusia and in two or more rows on either side of the mid-rib on the reduced pinnae that form the upper 1/3 of the fertile frond. Indusia are thick, entire and blackish when dry. Since the upper pinnae are quite small, the entire underside seems to be covered.
Fiddleheads are scaly and stout with silvery white scales, appearing among the recumbent green fronds of the prior year.
Habitat: Growth is from a large compact scaly creeping rhizome that is long-lived. It prefers moist well-drained rich soil, neutral to acidic. They tolerate shade well, but if in a lot of sun, the soil must be moist. Soil in winter should remain dry. Clumps can be divided in spring or fall. Christmas Fern is a good fern for beginners in fern culture.
Names: The common name comes from the use of this evergreen fern for decoration during the Christmas time. The genus, Polystichum, is derived from the Greek Words polys, meaning 'many, and stichos, meaning 'row' and together referring to the rows of sori on the type species for this genus. The species name, acrostichoides, is a reference to the genus Acrostichum where the sori form a solid mass on the back of the pinnae of the fertile frond - as they do here. The author names for the plant classification are as follows: First to publish was ‘Michx.’ which refers to Andre Michaux (1746-1802), French botanist who made many exploring expeditions in the U.S. collecting and cataloging many species. His notes were later used by his son, Francois, who with Thomas Nuttall published the multi-volume North American Sylva. Michaux's work was amended by ‘Schott’ who is Heinrich Wilhelm Schott (1794-1865), Austrian botanist who did extensive work on the Araceae family. His last position was director of the Imperial Gardens at Schönbrunn Palace in Vienna.
Above: Fiddleheads of Christmas Fern are stout and very scaly. 3rd photo - A mature sterile frond showing the distinctive 'leathery' appearance.
Below: 1st & 2nd photos - Fertile fronds have the abrupt decrease in size of the pinnae at the top 1/3 of the frond. Note (2nd photo) the scales on the rachis and the auricles pointing upward. 3rd photo - The sori almost cover the back side of the pinnae on the fertile fronds.
Below: 1st photo & large photo below - New fuzzy fiddleheads emerging in early April next to the prior years fronds. 2nd photo - Sori are oblong, tan colored. covered with a circular indusia and in two or more rows on either side of the mid-rib of fertile fronds, even covering the auricle.
Below: 1st photo - Christmas fern sterile fronds stay evergreen during the winter. Here you see the prior year fronds among the newly emerged fronds. 2nd photo - The margins of sterile pinna have spiny tipped teeth that curve upward. Note also the upward pointing 'ear' at the base of each pinna.
Below: The lowest pair of pinnae point downward away from the plane of the blade. Several pairs immediately above may do so as well.
Notes: Christmas Fern is not indigenous to the Garden. Eloise Butler originally planted it in Sept. 1908, sourced from Cambridge, Nova Scotia and again in Sept. 1909 with plants sourced in Appleton, ME, and again in 1911 and 1916. Curator Martha Crone planted 18 in 1934, more in 1938, '51 and '55. Then, when developing the Fern Glen she planted 55 in 1956 and 30 in 1957, all sourced from The Three Laurels, Marshall NC. Gardener Ken Avery planted it in 1963 and Curator Susan Wilkins planted some in 2006.
In the U.S. Christmas fern's range is the eastern half of the country from north to south. In Canada it is found in provinces from Ontario eastward. Minnesota is at the extreme north-western edge of its range and within Minnesota it is rare in the wild, being known only from Houston and Winona counties and as of Aug. 2013, is listed on the Department of Natural Resources' "Threatened List." It had not been found in Minnesota prior to 1979. Next door in Wisconsin it is on their "special concern" list.
There are 15 species of Polystichum found in North America, but only two known in Minnesota: P. acrostichoides, Christmas Fern, and Polystichum braunii (Spenn.) Fée, Braun's Holly Fern, which is on the state "Endangered List". Polystichum lonchitis, Northern Holly Fern, has been reported in the state by some publications, but according to the U of M Herbarium, that is probably a mis-identification as it has never been collected in the State.
Eloise Butler wrote: "The Christmas fern, so common farther east, but here an introduced species, takes kindly to the bog as well as to the rich black soil of the wooded slopes. It is sometimes mistaken for a short leaved variety of the cultivated Boston fern, but a comparison of the fruit dots on the backs of fronds will show the difference." from Liverworts, Lichens, Mosses, and Evergreen Ferns in the Wild Garden, ca. 1914.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"