Polypodium glycyrrhiza, or licorice fern, is a member of the Polypodiaceae family, which includes about 1200 species of ferns (Alden 1998). This perennial was given its name because of its licorice flavored rhizome. Native Americans used the strongly flavored rhizome for medicinal purposes, as well as for cooking and for sweetening foods (Pojar and MacKinnon 2004). Licorice fern is an evergreen pteridophyte with oblong pinnate fronds 5-12 inches in length that diminish in size further up the stalk, eventually narrowing into a point. Its leaflets are arranged in an opposite pattern and are bright green in color, shiny, fine-toothed, and broad-based (Alden 1998).
Licorice ferns have two rows of sori on the underside of each leaflet. Although the leaflets and stalk are consistently green, the sori are a golden-yellow color, which makes them stand out from the rest of the plant. During cool or humid weather, the fern’s spores are released in hopes of reproducing in more locations. One of Polypodium glycyrrhiza’s distinctive qualities is the fact that each frond grows separately from a reddish-brown rhizome, as opposed to other ferns, which have multiple fronds growing from one site on a rhizome (Brietzke and Starzomski 2013).
Licorice fern is native to western North America and is concentrated in areas such as southern Alaska, southwestern Yukon Territory, western British Columbia, Washington, Oregon, Idaho, and California. Some researchers (e.g., Klinkenberg 2015) mention the existence of a disjunct population in Arizona, however Flora of North America proposes that these reports were based on misidentified specimens (Flora 2016). Throughout its range, licorice fern generally grows at low elevations below 1,800 feet (Kaczynski 2005). Its preferred locations show that it likes temperate regions that tend to have wet winters and cool, moist summers. Polypodium glycyrrhiza typically grows as an epiphyte on broadleaf trees and rocks in lowlands and can also form sheets over rocks and trees. However, it has also been found to grow on the ground, as well as on fallen trees. Licorice fern is particularly fond of growing on Acer macrophyllum, commonly known as bigleaf maple.
Polypodium glycyrrhiza, commonly known as licorice fern, many-footed fern, and sweet root, is a summer deciduous fern native to western North America, where it is found in shaded, damp locations.
Spores are located in rounded sori on the undersides of the fronds, and are released in cool weather and high humidity.
Licorice fern grows single fronds scattered along a thick creeping rhizome; the genus name Polypodium (many-footed) refers to this characteristic. The fronds are once-divided and triangular in shape, with finely-toothed margins and pointed leaflets. They are usually at least one foot in length, but may grow to be over two feet long, and may be much smaller when growth conditions are less ideal. They also display parallel venation. When sori are present on the leaf underside, they correspond with small bump-like protrusions on the top side of the leaves. The rhizome is creeping and the fronds appear to have random placement, originating at various points. The rhizome appears reddish-brown, and has a sweet licorice flavor. Since it is a fern, P. glycyrrhiza reproduces by spores; the spores form in two rows of sori, which look like large spots on the undersides of the leaves. The sori range in color from yellow to orange to brown. Plants that are not thriving may have no sori or the sori may be patchy and will not appear in neat rows. Licorice fern may grow over the ground, rocks, or as an epiphyte, especially on moss-covered Acer macrophyllum.
The species is not closely related to the flowering plant from which the commercial product licorice is derived (Glycyrrhiza glabra).
The specific epithet glycyrrhiza refers to the pronounced licorice flavor of the rhizome. Glykys in Greek means sweet, while rhiza means root.[1]
It occurs primarily in a narrow near-coastal strip in southern Alaska, southwestern Yukon Territory, western British Columbia, Washington, Oregon, and California, with a disjunct population in Idaho.[2]
The plant prefers moist environments, so it is typically found on wet ground, rocks, moss-covered tree trunks in very wet areas, and logs. Occasionally it can be seen on fallen trees. It is particularly associated with bigleaf maple (Acer macrophyllum).[3][4] The fern is mycorrhizal, meaning it can form root associations with the hyphae of fungi.[5] It takes advantage of the mild, wet winters and the substrate of deciduous trees to photosynthesize and grow during the cold season when most other temperate plants are dormant. Habitat elevation is lowlands below 600 meters.[6]
The sweet flavor of the rhizome was once attributed to the glycoside glycyrrhizin. However, a study has shown that the flavor may actually be due to polypodoside, which is 600 times sweeter than 6% sucrose solution.[7]
Licorice fern is cultivated as an ornamental garden plant. The cultivar 'Longicaudatum' has gained the Royal Horticultural Society's Award of Garden Merit.[8][9]
Licorice fern was chewed for flavor by numerous Native American groups, including the Squamish, Shishalh, Comox, Nuxalk, Haida, and Kwakwaka'wakw. The rhizomes were also usually used medicinally as a treatment for the cold and sore throats.[10][3][11]
Growing on log
Rhizome close-up
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Fronds with and without spores
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Young frond
Growing on moss-covered big leaf maple
Polypodium glycyrrhiza, commonly known as licorice fern, many-footed fern, and sweet root, is a summer deciduous fern native to western North America, where it is found in shaded, damp locations.
Spores are located in rounded sori on the undersides of the fronds, and are released in cool weather and high humidity.
