Shape: Marginal Fern is an erect fern, growing in scattered clumps in woodland settings. The upright arching green fronds grow from 10 to 40 inches in height with various old withered fronds at their base. The current years fronds will remain green overwinter (although flattened by snow load) and not dry up until the next years fronds are fully grown - as Eloise Butler said - "doing duty the whole year round."
Fronds: Fronds are bluish-green above, light green under, retaining their color through the winter. The blades are ovate to lanceolate, up to 10 inches wide, widest about half of the way up from the base with the tip usually arching. There are no aromatic glands. Fronds are leathery, and die back after new fronds are formed in Spring. Sterile fronds look the same. The central rachis is green with pale-tan small scales on the underside. The grooved stipe is 1/4 to 1/3 the length of the frond. The tawny scales on the stipe are dense and in tufts.
Pinnae: The pinnae are lance shaped and on larger fronds rapidly taper to tips which typically turn upward. Pinnae are mostly in the plane of the blade, not tilted, and may have a very short stalk. The division pattern is pinnate-pinnatifid to bi-pinnate near the base. On the rachis, the pinnae are sub-opposite each other (slightly offset). The upper side of the costa is grooved but the groove does not meet the groove on the rachis. There may be 15 to 20 pairs of pinnae on the rachis.
Pinnules: There will be 20+/- pairs of short pinnules. Margins of the pinnules are entire or slightly lobed without teeth. Pinnule tips are blunt. There is a distinguishing difference in length of the adjacent basal pinnules. First, the basal (inner-most) pinnules are typically longer than those above it (toward the tip of the pinna) on the same side of the pinna costa. Second, the lower basal pinnule (the basiscopic pinnule) is longer than the opposing upper pinnule (the acroscopic pinnule). See examples in the second pair of photos below.
Fertility: The sori are placed on the back of the pinnule near the pinnule margin, either single or in a single well spaced row on either side of the pinnule. Sori are rounded with a kidney shaped indusia covering them, without glands.
Habitat: Marginal Fern grows from a stout ascending rhizome that is covered with bright shiny scales. It is found in rocky wooded slopes, woodland edges and ravines in partial shade and based on the Minnesota population, also in sunny stony bluffs and ridges. Soils can be acidic, neutral or alkaline. It forms a nice clump but is not an aggressive spreader. D. marginalis hybridizes with other species but hybrids have malformed spores and position of sori not quite marginal.
Names: Marginal Fern gets its common name from the position of the sori on the underside margin of the pinnules. The genus name Dryopteris, is derived from two Greek words, drys, meaning 'tree,' and pteris, meaning 'fern.' Many members of this genus are commonly referred to as "wood" ferns and hence the name. The species, marginalis, meaning 'margined,' refers to the sori placement.
The author names for the plant classification are: The first to publish information, in 1753, was '(L.)' which refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. His work was amended in 1848 by ‘A.Gray’ who is Asa Gray (1810-1888), American botanist, Professor of Natural History at Harvard and instrumental in unifying plant knowledge of North America and author of Gray’s Manual - Manual of the Botany of the Northern United States, from New England to Wisconsin and South to Ohio and Pennsylvania Inclusive.
At first the plant was first classified as Polypodium marginale by Linnaeus, then Aspidium marginale in 1806 and finally reaching D. marginalis in 1848, although in Eloise Butler's time the prior classification was still much used.
Comparisons: There are many species of wood ferns with 14 in North America alone. Other members of the Wood Fern Family are Spinulose Woodfern, Dryopteris carthusiana; the Crested Wood Fern, Dryopteris cristata; Male Fern, Dryopteris filix-mas; and Goldie's Fern, Dryopteris goldiana. The key to Marginal Fern is 1) no aromatic glands, 2) blades pinnate-pinnatifid to bi-pinnate with the pinnules having margins entire or slightly lobed, no teeth, and a blunt tip, 3) different lengths of the basal pinnules, 4) dense brown scales of a single type on the stipe, 5) pinnae lance-like, long and rapidly tapering to the tip, 6) large sori at the margin of the pinnae, 7) fronds leathery and evergreen with older withered fronds at the base.
Above: A frond - widest about the middle, leathery, opposite pinna slightly offset. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 1st photo - The upper side of a pair of smaller pinnae - note the bluish-green color and the groove on the upper side of the pinna costa and the central rachis; also note the placement of pinnae on opposite sides of the rachis is sub-opposite. 2nd photo - The under side of the pinna. Note - the basal pinnules (closest to the central rachis) are larger than the others and the lower basal pinnule is longer than the basal upper pinnule.
Below:The sori are along the margins of the pinnules. 1st photo - immature sori, 2nd photo - maturing sori. Note the kidney shaped white indusia.
Below: 1st photo - the tawny scales of the stipe. 2nd photo - Fiddlehead.
Below: The remains of the prior years fronds, flattened by snow load, are still at the base of the new fronds in June. Note the thick scales on the stipes of the new fronds.
Notes: Marginal Fern is not indigenous to the Garden. Eloise brought in the first plants in September 1908 from Bear Mountain, Mass. In 1909 she brought in more from the same source. Six from Gillett's Nursery in Southwick Mass in 1918. In Miss Butler's day she was using the now unaccepted name of Aspedium marginale, although D. marginalis had already been assigned in 1848. Martha Crone added additional plants in 1934 obtained from Ferndale Nursery in Askov Minn. More were planted in 1955 and in 1956 she added 55 plants from The Three Laurels, in Marshall NC, when she was developing the Fern Glen.
Marginal Fern is quite rare in Minnesota. It was not discovered in the State until 1981 when some were found in Houston County. Since then a smaller group was found in neighboring Filmore County. The fern was elevated from "Threatened" to the Minnesota DNR "Endangered Species List" in 2013. The range of Marginal Fern in North America is generally east of Minnesota from the Mississippi River to the east coast, excepting Florida and Louisiana. In Canada it is reported in all provinces from Ontario eastward and has also been found in Greenland.
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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"