Polypodium glycyrrhiza, commonly known as licorice fern, many-footed fern, and sweet root, is a summer deciduous fern native to western North America, primarily in a narrow strip in southern Alaska, southwestern Yukon Territory, western British Columbia, Washington, Oregon, and California, though two highly disjunct populations are known from Idaho and Arizona. It thrives in a humid climate, prevailing in areas with cool and moist summers and warm and wet winters. P. glycyrrhiza can often be found growing on the trunks and branches of winter deciduous trees, particularly bigleaf maple, but is also often found on rocks, logs, and wet, mossy humus. 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.
Licorice fern acquires its name from its licorice-flavored rhizome, which 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.
Spores are located in rounded sori on the undersides of the fronds, and are released in cool weather and high humidity.
This species is a diploid, and is one parent of several species of hybrid origin:
- Polypodium vulgare (with Polypodium sibiricum)
- Polypodium hesperium (with Polypodium amorphum)
- Polypodium calirhiza (with Polypodium californicum)
Licorice fern does not grow its fronds from a centralized location; this is contrast to other ferns that grow their fronds from the same spot. The name Polypodium refers to this characteristic—it means "many-footed." 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. They also display parallel venation. The rhizome is creeping and the fronds appear to have random placement, originating at various points. The rhizome appears reddish-brown, and is a sweet licorice-flavored. The name glycyrrhiza refers to this flavor--glykys in Greek means sweet, with rhiza meaning root. Since it is a fern, P. glycyrrhiza reproduces by spores; the spores grow in a pattern of spots on the undersides of the leaves. These sori may be oval in immaturity. Licorice fern may grow over the ground, rocks, or as an epiphyte. The plant prefers moist environments, so it is typically found on wet ground, rocks, and logs. Occasionally it can be seen on fallen trees. It is very often associated with Acer macrophyllum. The fern is mycorrhizal, meaning it can form root associations with the hyphae of fungi.
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.
The licorice fern is sometimes valued for its licorice-flavored rhizome. Occasionally it is chewed, and it can also be brewed into a licorice-flavored tea. It may be used as a medicine for colds and respiratory conditions by indigenous peoples. It is considered an important medical plant and may have been used similar to cough drops. Since the rhizome is so sweet even in its naturally occurring state, and since the chemical is not a saccharide, it is possible that this compound could be used as a natural alternative to traditional sweeteners.
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