Polypodium L. (family Polypodiaceae) is a cosmopolitan genus of ferns commonly known as polypodies. The genus was established by Linnaeus in his Species Plantarum (1753) and currently encompasses around 47 accepted species and 8 natural hybrids according to the Checklist of Ferns and Lycophytes of the World, though GBIF documents over 340 taxa across the broader aggregate.
Polypodies are terrestrial or epiphytic ferns characterised by slender to stout, long-creeping rhizomes that are densely covered with hair-like scales, from which fronds emerge at intervals. The fronds are typically evergreen, persisting one to two years, and range from 10 to over 80 cm in length. Blades are usually pinnate or pinnatifid — divided into linear-oblong to linear-triangular lobes — though simple forms occur. Venation is generally free, occasionally forming simple areoles. The most distinctive feature is the naked, globose sorus (spore cluster) which lacks the protective indusium found in many other fern families.
The genus has its highest species diversity in the tropics but extends from subarctic regions to equatorial zones, occurring on every inhabited continent. Members grow most commonly on rock surfaces, occasionally on the ground or as epiphytes on tree bark and moss mats.
Etymology
The genus name Polypodium is derived from two Ancient Greek words: poly ("many") and podion ("little foot"). The name refers to the foot-like appearance of the rhizome as it branches and spreads, each attachment point resembling a small foot. The common name "polypody" is a direct anglicisation of the Latin genus name.
Distribution
Polypodium is one of the most widely distributed fern genera in the world, occurring on every inhabited continent from subarctic latitudes to equatorial rainforests, with peak species diversity in the tropics. In North America, the genus is well represented across the Pacific Northwest (P. glycyrrhiza, P. amorphum, P. scouleri), the Appalachians (P. appalachianum, P. virginianum), the Southwest (P. hesperium, P. aztecum in Arizona), and along the California coast (P. californicum). European representatives include P. vulgare and P. cambricum, documented across the continent including four taxa confirmed in Switzerland. The Pacific Northwest species P. glycyrrhiza extends north to Alaska, the Aleutian Islands, and Kamchatka.
Ecology
Polypodies most often colonise exposed rock surfaces — cliff faces, boulders, and rocky woodland floors — and are also frequent epiphytes on moss-covered tree trunks and branches. They occasionally grow terrestrially in humus-rich woodland soils. The rhizome's creeping habit allows the plant to spread gradually across suitable substrates. Fronds are typically evergreen, persisting one to two years before being replaced, which gives the plants a year-round presence even in temperate climates. The genus includes both diploid species and allopolyploids formed by interspecific hybridisation, and natural hybrids are frequently documented within regions where two or more species co-occur.
Cultivation
Several Polypodium species and cultivars are grown as ornamental plants, valued for their shade tolerance, evergreen foliage, and the architectural texture of their fronds. Cultivars such as Polypodium 'Green Wave' are used in shaded garden settings. Polypodies prefer moist, well-drained soils rich in organic matter and bright filtered or dappled light, though they tolerate short dry spells and occasional direct sun. They are well suited to rock gardens, drystone walls, and the base of woodland trees. Polypodium glycyrrhiza is hardy across USDA zones 6-9.
Cultural uses
Native peoples of the Pacific Northwest made extensive use of Polypodium glycyrrhiza (licorice fern). The rhizomes, which have a distinctly sweet, liquorice-like flavour, were chewed as a pleasant confection and used as an appetiser, particularly for children. Medicinally, the rhizomes were employed for a wide range of chest complaints — coughs, colds, sore throats, and chest pain — administered by chewing, as an infusion, or brewed as a tea. The rhizome is described in ethnobotanical literature as alterative, carminative, haemostatic, and pectoral. More broadly, polypodies have a documented history of use as a culinary spice with a bitter-sweet character, including use in nougat preparation in parts of Europe.
Taxonomy
Polypodium L. was formally described by Carl Linnaeus in Species Plantarum (vol. 2, p. 1082) in 1753, making it one of the earliest fern genera named under the Linnaean system. Under the Pteridophyte Phylogeny Group (2016) classification, it is placed in family Polypodiaceae, subfamily Polypodioideae, order Polypodiales, class Polypodiopsida.
The genus has undergone significant circumscription changes. Many species formerly included in Polypodium have been transferred to related segregate genera (e.g. Phlebodium, Microsorum, Pleopeltis), and the current accepted count is approximately 47 species. North American polypodies form a complex network of diploid species and allopolyploid derivatives with reticulate evolutionary relationships distinct from the European P. vulgare group. In Switzerland, four taxa are recognised: P. cambricum, P. interjectum, the hybrid P. interjectum x vulgare, and P. vulgare sensu stricto. Hybrid formation is common in the genus worldwide.
Propagation
Polypodium can be propagated by spores or by division. Spores should be sown fresh on humus-rich, sterilised soil in a pot sealed under plastic film to maintain humidity, and kept in a warm, bright position out of direct sun until the prothalli develop. Division of established clumps in spring is a straightforward method: sections of rhizome bearing healthy fronds are separated and replanted at the same depth, kept moist until re-established.
