Green Mountain Maidenhair Fern
by Erin Schaeffer, Marylee Everett Fellow 2010
As an intern for the Conservation Department at New England Wild Flower Society, I have had the opportunity to explore the northeastern woods and wetlands in search of rare plants. With a background in architecture, my trained eye is attracted to the unique geometric forms of ferns and has enticed me to pursue a challenge to differentiate among and learn more about these non-flowering forms. Little did I know that the identification of ferns most often requires us to stop and take critical look at extremely small identifying characteristics such as the number of cuts in a frond; the presence, size, and position of sori, scales, and glandular hairs; vein patterns and more!
However, maidenhair ferns (Adiantum spp.) are strikingly unique and easily recognizable. The stipe, rachis and costa, all of which are stems, resemble thin shiny black wires that support a long, semi-circular patterned leaf, known as a blade. This particular geometric form is the most common indicator of the maidenhair genus. Upon closer examination the blade is subdivided into two rachis branches. Each branch is usually comprised of five to six leaflets called pinnae, which are further divided into many individual wing-like or fan-shaped structures called pinnules. The edges of each pinnule tend to curl under to create a false indusia, or cover, to protect masses of underlying spore cases known as sori. There are no scales or glandular hairs on the maidenhair species, but another indicative characteristic is multiple forked veins on each pinnule.
Like any architectural structure, context helps build a more complete understanding of the maidenhair species. In1905, American botanist Merritt Lyndon Fernald made an important observation that has since driven current day studies of maidenhair ferns. He observed that the northern maidenhair fern and western maidenhair fern were exclusively limited to an uncommon soil type. Geologically, the soils, in which these maidenhair ferns were observed to grow, are shallow serpentine substrates that contain high levels of nickel, iron, chromium, and cobalt and lack common elements that are essential for most plants including calcium, phosphorus, nitrogen, and potassium. Through my light geological research using R.R. Brooks Serpentine and Its Vegetation, I came across the interesting observation that serpentine soils create a microclimate of their own. According to Brooks, this substrate tends to be porous, allowing root structure aeration, and dark hued soil, colored by high levels of iron, is responsible for localized temperature extremes due to radiant heat loss and gain.
Armed with historic ecological observations and technology for genetic investigation from the 1980s to the present, researchers have studied differences among eastern North American maidenhair ferns based on life-cycle events that are influenced by habitat variation. Through extensive exploration in the field and laboratory, it was confirmed that instead of just two species of maidenhair ferns in eastern North America there are actually three! The third named species is the Green Mountain maidenhair fern (A. viridimontanum), which is genetically a hybrid between the northern maidenhair fern (A. pedatum) and western maidenhair fern (A. aleuticum). In 1991, researcher Catherine Paris from the University of Vermont formally described green mountain maidenhair fern as a new species.
Currently, the Green Mountain maidenhair fern is listed as a globally rare species with 21 current, observed locations and is endemic to Vermont and Quebec. This species is globally rare due to its severe habitat restrictions and is most threatened by asbestos mining, road expansion, and over-collection. Further species challenges include the disturbance of unique ecological processes that are specific to serpentine soil plant communities including hydrology and light availability. Fortunately, due to its restricted habitat location on steep talus slopes and heavy metal laden serpentine soils, the Green Mountain maidenhair fern is not severely threatened like so many other rare and endemic plants by the most common human disturbances: agriculture, forestry, and land development. Ongoing research is occurring to better understand the distribution of this fern and its unique habitat restrictions.
If you would like to view this unique species and many others please come and explore Garden in the Woods in Framingham, Massachusetts.