What do swords and licorice have in common? If you live on the wet side of the Pacific Northwest you’ll recognize immediately that these are two of our common ferns that stay green all winter.
I went for a walk on one of my favorite forest trails out at the Stimpson Family Nature Preserve on the afternoon of New Year’s Eve and the ground was carpeted with sword ferns, Polystichum munitum. Licorice ferns, Polypodium glycyrrhiza, while not nearly as prolific were still abundant growing among the moss on many bigleaf maple trunks. Our other evergreen fern is deer fern, Blechnum spicant, but it’s not as plentiful in my neighborhood woodland. I’ll share that one another month.
It’s almost impossible to visit any woodland on the west side of the Cascades and not come across both of these ferns.
Sword ferns are found from Alaska all the way down to California and east to Montana and Idaho according to the USDA Plants database. In some forests they carpet the ground almost completely, forming a dense green layer under the tall conifers. It’s an extremely shade-tolerant fern, but will also continue to grow after the forest has been clear cut. On sunny sites the fronds are generally smaller and held more erect.
That ability to grow in a variety of habitats makes sword fern a good choice for many gardens. It transplants and divides easily (by shovel pruning). It will grow best in a fairly rich soil high in humus, but they’re reasonably happy in the ordinary garden soil in my shady border among a dogwood, azaleas, and rhododendron.
Sword ferns can get large, with individual fronds reaching nearly three feet in length under ideal conditions. Two feet is more typical, but with its arching habit you’ll want to give each plant plenty of room. In the wild they usually space themselves around six feet apart.
In its native habitat sword fern is an important browse for wildlife, including Roosevelt elk, deer, and black bear.
Sword fern generally reproduces sexually in the wild from spores produced on the underside of most fronds. As with other ferns, the reproductive cycle is complex with the first generation being a bisexual gametophyte that has no vascular system, requires a very moist environment, and doesn’t look at all like the spore-bearing mature plant. You can find more details about sword ferns, including habitat, fire ecology, and plant associations on a US Forest Service Polystichum munitum web page.
Some gardeners find the previous year’s fronds to be unsightly in late spring as the new fronds are emerging and unfurling. The old fronds can be cut off and composted, helping to keep the garden looking a bit more neat and tidy. Personally, I don’t bother and the old fronds disappear on their own by mid-summer.
More photos of sword ferns are on my wildflowers website, showing them in several forest understories and trailside habitats.
While sword ferns grow on the ground, licorice ferns are usually found growing out of the moss that clings to the trunks of hardwood trees, particularly bigleaf maple.
However, Polypodium glycyrrhiza is not strictly arboreal. I’ve also seen it growing on moss-covered boulders and in a garden at the side of some stone steps. According to the USDA Plants database licorice fern is found all along the west coast from Alaska to California.
Licorice fern gets its common name from the flavor of the underground rhizome. The rhizome contains a natural sweetener, polypodoside A, that is roughly 600 times sweeter than sugar. To my taste it’s not that sweet (although it may be that the concentration is pretty low) but it definitely tastes like licorice. It’s a fun plant to introduce to kids on the trail. They’re always amazed when I carefully pull out a small piece of the rhizome and hand it around for a taste. Traditionally it’s been chewed for the flavor and also used as medicine for colds and sore throats.
Some casual observers confuse sword ferns and licorice ferns because they both have arching fronds and can sometimes be found in similar habitats.
A close examination of the way the individual pinnae are attached to the rachis is an easy way to tell them apart. Sword fern pinnae are attached at a single point and the base of each pinnae resembles the scabbard of a sword. Licorice fern pinnae are attached along the entire base, with adjacent pinnae almost growing together.
I have a few additional photos of licorice fern on my wildflowers website. You can see it growing both on a rocky site and among moss on a tree trunk.
Licorice fern is summer deciduous in most places. That is, when days get hot and the rains stop it dries up. Walking through the forest on a late-August day you’d think the licorice ferns had all died. However, when autumn rains return the ferns quickly put out fresh foliage that remains green all winter long and into the beginning of the next summer.
Both of these evergreen ferns are good choices for a woodland garden in the wet areas of the west coast. Sword fern is perhaps easier to establish as it accepts a wider variety of conditions. Licorice fern, since it grows on moss-covered maple or alder trunks in the wild, needs a similar habitat in the garden.
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