Shape: Glade Fern is a large fern of rich forests and slopes; with narrow fronds that rise in almost circular clusters of 5 to 6 fronds from the root, growing 2 to 3+ feet tall.
Fronds: Fronds are bright green, either sterile or fertile. The sterile fronds rise first and arch over, 18 to 40 inches long and only 5 to 10 wide, but not reaching the vertical height of the later fertile fronds which arise in Summer. The blades are narrow, lance shaped with a slightly narrowed base and taper to a pointed tip. Fronds bear 20+/- pairs of narrow alternate pinnae. The visual difference between the fronds that have fertile sori and those that are sterile is the fertile are higher and less arching and the pinnae are narrower. There are no aromatic glands. The central rachis is green with a deep groove on the upper side; this groove continues into the the costa of each pinnae. The stipe is shorter than the blade, 6 to 16 inches long - approximately 1/3 the total frond length. The lower part of the stipe may be a reddish straw color at the base and slightly scaly, but green to yellow-green above, without hair or numerous scales.
Pinnae: The pinnae are narrow, up to 3+ inches long and 1/2 inch wide, long, sharp-tipped, rounded to heart-shaped at the base; only the lower pinnae will have short stalks. They are alternate on the rachis, without lobes or teeth, margins wavy. Sterile pinnae are less stiff than the fertile ones.
Pinnules: None- the blade is only pinnate.
Fertility: The sori are evenly spaced on the back of the fertile pinnae from near the mid-vein to almost the tip; these are long, narrow, slightly curved, in a single row, in herringbone fashion on one side of the lateral vein, never across the veins (The lateral veins are thin and visually this looks like vein - sori - vein - vein - sori - vein - vein and repeating. See photos). Sometimes these may be doubled - one on each side of the vein in which case there is no visual gap between lateral veins (and the pattern is sori - vein - sori - vein, etc). They have an indusia covering them. As the sori mature, the indusia is lifted giving the appearance of vault. Sori turn dark brown when ripe.
Habitat: Glade Fern grows from a short, scaly, creeping rhizome in rich soil, in partial to full shade, doing best in moist well-drained soils. Fronds will turn brown if the soils dry out. Because the plant is long-lived the clump can be difficult to move. Offshoots from the rhizome can form colonies over time and propagation can be done by root division.
Names: Glade Fern is named for the habitat where it is found. The genus name Diplazium, is derived from two Greek words, di, meaning 'two' or 'double', and plasion, meaning 'oblong', both together meaning 'doubled oblong sori' but in this species of Diplazium that doubling seldom happens of . The species pycnocarpon is likewise, from two Greek words: pyknŏs meaning "dense" and karpos meaning 'fruit'; together referring the dense sori on the pinnae. The many members of the Dryopteridaceae are commonly referred to as "wood" ferns. There are three older scientific names as the species was formerly in two other genus and their names were - Asplenium angustifolium, Asplenium pycnocarpon and Athyrium pycnocarpon. It was in the first genus - the Spleenworts - that the plant picked up the common name of Narrow-leaved Spleenwort, but the species was moved to the new genus since it is lacking the spleenwort characteristics.
The The author names for the plant classification are: The first to publish information in 1804 under the name Asplenium pycnocarpon was ‘Spreng.’ which refers to Kurt Polycarp Joachim Sprengel (1766-1833) German botanist who is noted for his early studies of the fertilization of flowers by insects. His work was not complete and was amended by ‘M. Broun’ which refers to Maurice Broun, Orleans Mass., who in 1938 published Index to North American Ferns.
Comparisons: There are many wood ferns but in our area the most closely confusing may be the Christmas fern, Polystichum acrostichoides which also has long pointed pinnae, but there the fronds are more leathery, there are basal lobes on the pinnae and the upper section of fertile fronds is considerably narrowed compared to the pinnae below them on the frond.
Above: A frond showing the alternate placement of the pinnae, the overall lance-shape, and pointed tip. The individual pinna are of similar shape.
Below: 1st photo - The upper side of a pinnae; the base is shallowly heart-shaped, the margins wavy - note the deep groove on the central rachis. 2nd photo - the underside of the pinnae; the lateral veins fork and there is slight fine hair on the costa (central rib).
Below: Stipes have some reddish color near the base but above are green with few scales.
Below: DEVELOPMENT OF SORI: Three views in the successive development of the sori. 1st photo - just beginning to develop, the indusia a lighter color than the pinnae. Note they attach on one side of the lateral vein. 2nd photo - approaching maturity. 3rd photo - mature sori showing the characteristic 'vaulted' appearance.
Below: Glade fern forms a nice clump. By the time the sori are maturing, the fertile fronds may be arched over just like the sterile fronds.
Notes: Glade Fern is not indigenous to the Garden. Eloise Butler introduced it when she brought in plants on May 17, 1911 from Gillett's Nursery of Southwick Mass. She used the name Asplenium angustifolium. It was regularly planted after that. Eloise planted in 1912, '18, ' 20, and '31. Curator Martha Crone planted in 1937, '39, '53, '54, '55, and planted 20 in 1957 when she was developing the Fern Glen. The latter were sourced from The Three Laurels, in Marshall NC. There were no further plantings after that. The range of the fern in North America is the eastern half, excepting along the gulf coast states of the U.S., Maine and the Canadian Maritime provinces. Minnesota and Ontario are on the western edge of the range.
Rarity: Glade Fern is rare enough in the wild in Minnesota that it is listed on the Minnesota DNR "Threatened" list. According to the MN DNR surveys it is known only in 4 counties in the driftless SE section of the State. Three species of the genus Diplazium are found in North and Central America, but the other two are outside of Eastern North America.
Frances Theodora Parsons wrote in 1899 "Late in August the plant has reached a stately height, perhaps of three or four feet. The fronds are still smooth and delicate to a degree unusual even in ferns. But they wear a deeper green, and their texture seems a trifle more substantial. Occasionally, though rarely in the deeper woods, we find a frond which is conspicuously longer-stalked, taller, narrower than the others, with pinnae more distant and more contracted. A glance at its lower surface discovers double rows of brown, linear fruit-dots.
Though one of the largest of its tribe, the Narrow-leaved Spleenwort suggests greater fragility, a keener sensitiveness to uncongenial conditions, than any other of our native ferns. A storm which leaves the other inhabitants of the forest almost untouched beats down its fronds, tender and perishable even in maturity. This very fragility, accompanied as it is with beauty of form and color, in the midst of the somewhat coarse and hardy growth of the August woods, lends the plant a peculiar charm." From A GUIDE TO THE NAMES, HAUNTS, AND HABITS OF OUR COMMON FERNS
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"