Pioneer Valley Fern Society

2022-2023 Winter Ferns

#8 & 9 Common & Appalachian Polypodies

I thought it would be better if we did these two polypodies at the same time, for an easier to see comparison. The Common or Rock Polypody (Polypodium virginianum) on the left in the photo is the one that we see most often in our area. But we do occasionally find nice patches of Appalachian Polypody (Polypodium appalachianum) as well. While both are found throughout the Northeast, Common Polypody extends to the south and west to northwest of the country and Canada. Appalachian Polypody is mostly eastern US and Canada. These are the only two species in our Northeast area.

Their leathery leaves are vibrant green throughout the year, which I especially appreciate in winter. They grow in colonies on top of rock outcrops and boulders. There are several quotes from Henry David Thoreau about the Polypody ferns, including a long one in the front of Steve Chadde's book (Northeast Ferns). A short quote from Thoreau describes them well, "Fresh and cheerful communities of the polypody form a lustrous mantle over rocky surfaces in the early spring".

The Common Polypody is identified from the Appalachian by having a blade that is generally oblong or lance-shaped and widest in the middle, while the Appalachian is more triangular in shape, widest at the base. The pinnae (leaflets) of the Appalachian Polypody are much more pointed at the tips. The Common Polypody has more rounded or blunt tips, as you can see in the photo. However, it should be noted that you may see some polypodies that are somewhat triangular in shape but have very blunt tips. There are hybrids out there! Usually they have a range of features in one patch, and are not all consistently triangular or lanceolate, with pointed or blunt tips.

Both polypodies have beautiful large yellow to brown sori on most of the pinnae (leaflets), which can often be seen throughout the year. The polypodies can be easily differentiated from Christmas Ferns because the Polypody blades are "pinnatifid", meaning the blades are deeply lobed and cut almost to the rachis (stem) but remain attached to each other. The pinnae of the Christmas fern are attached separately to the rachis (and have shapes that may look like a Christmas stocking or sleigh sideways). Christmas Ferns also have different fertile fronds, which are taller than the sterile ones, with narrow brown tips of the blades. The fertile and sterile fronds are the same for both the Common and Appalachian polypodies.

As a final note, Steve Chadde (Northeast Ferns) states that the rhizome of the Common Polypody "has a strong licorice taste", while Go Botany's page on Appalachian Polypody states that their stems are "acrid tasting". I have not tried tasting them.

Thanks to Randy for the great photo used in this article. Taken Tuesday in the Mt Toby Waterfall area, Leverett.