Smith's Classification

The complete classification scheme proposed by Smith et al. (2006; alternative names in brackets):

• Class Psilotopsida
  • Order Ophioglossales
    • Family Ophioglossaceae (incl. Botrychiaceae, Helminthostachyaceae)
  • Order Psilotales
    • Family Psilotaceae (incl. Tmesipteridaceae)
• Class Equisetopsida [=Sphenopsida]
  • Order Equisetales
    • Family Equisetaceae
• Class Marattiopsida
  • Order Marattiales
    • Family Marattiaceae (incl. Angiopteridaceae, Christenseniaceae, Danaeaceae, Kaulfussiaceae)
• Class Pteridopsida [=Filicopsida, Polypodiopsida]
  • Order Osmundales
    • Family Osmundaceae
  • Order Hymenophyllales
    • Family Hymenophyllaceae (incl. Trichomanaceae)
  • Order Gleicheniales
    • Family Gleicheniaceae (incl. Dicranopteridaceae, Stromatopteridaceae)
    • Family Dipteridaceae (incl. Cheiropleuriaceae)
    • Family Matoniaceae
  • Order Schizaeales
    • Family Lygodiaceae
    • Family Anemiaceae (incl. Mohriaceae)
    • Family Schizaeaceae
  • Order Salviniales
    • Family Marsileaceae (incl. Pilulariaceae)
    • Family Salviniaceae (incl. Azollaceae)
  • Order Cyatheales
    • Family Thyrsopteridaceae
    • Family Loxomataceae
    • Family Culcitaceae
    • Family Plagiogyriaceae
    • Family Cibotiaceae
    • Family Cyatheaceae (incl. Alsophilaceae, Hymenophyllopsidaceae)
    • Family Dicksoniaceae (incl. Lophosoriaceae)
    • Family Metaxyaceae
  • Order Polypodiales]])
    

    Adiantum lunulatum from Family Pteridaceae
    • Family Lindsaeaceae (incl. Cystodiaceae, Lonchitidaceae)
    • Family Saccolomataceae
    • Family Dennstaedtiaceae (incl. Hypolepidaceae, Monachosoraceae, Pteridiaceae)
    • Family Pteridaceae (incl. Pellaeaceae, Adiantaceae, Ceratopteridaceae, Cryptogrammaceae)
    • Family Aspleniaceae
    • Family Thelypteridaceae
    • Family Woodsiaceae (incl. Athyriaceae, Cystopteridaceae)
    • Family Blechnaceae (incl. Stenochlaenaceae)
    • Family Onocleaceae
    • Family Dryopteridaceae (incl. Aspidiaceae, Bolbitidaceae, Elaphoglossaceae, Hypodematiaceae, Peranemataceae)
    • Family Oleandraceae
    • Family Davalliaceae
    • Family Lomariopsidaceae (incl. Nephrolepis)
    • Family Polypodiaceae (incl. Drynariaceae, Grammitidaceae, Gymnogrammitidaceae, Loxogrammaceae, Platyceriaceae, Pleurisoriopsidaceae)
    • Family Tectariaceae

Economic uses

Ferns are not as important economically as seed plants but have considerable importance. Some ferns are used for food, including the fiddleheads of bracken, Pteridium aquilinum, ostrich fern, Matteuccia struthiopteris, and cinnamon fern, Osmunda cinnamomea. Diplazium esculentum is also used by some tropical peoples as food.

Ferns of the genus Azolla are very small, floating plants that do not look like ferns. Called mosquito fern, they are used as a biological fertilizer in the rice paddies of southeast Asia, taking advantage of their ability to fix nitrogen from the air into compounds that can then be used by other plants.

A great many ferns are grown in horticulture as landscape plants, for cut foliage and as houseplants, especially the Boston fern (Nephrolepis exaltata). The Bird's Nest Fern, Asplenium nidus, is also popular, and the staghorn ferns, genus Platycerium, have a considerable following.

Several ferns are noxious weeds or invasive species, including Japanese climbing fern (Lygodium japonicum), mosquito fern and sensitive fern (Onoclea sensibilis). Giant water fern (Salvinia molesta) is one of the world's worst aquatic weeds. The important fossil fuel coal consists of the remains of primitive plants, including ferns.

Ferns have been studied and found to be useful in the removal of heavy metals, especially arsenic, from the soil^[3]

Other ferns with some economic significance include:

• Dryopteris filix-mas (male fern), used as a vermifuge, and formerly in the US Pharmacopeia; also, this fern accidentally sprouting in a bottle resulted in Nathaniel Bagshaw Ward's 1829 invention of the terrarium or Wardian case
• Rumohra adiantoides (floral fern), extensively used in the florist trade
• Osmunda regalis (royal fern) and Osmunda cinnamomea (cinnamon fern), the root fiber being used horticulturally; the fiddleheads of O. cinnamomea are also used as a cooked vegetable
• Matteuccia struthiopteris (ostrich fern), the fiddleheads used as a cooked vegetable in North America
• Pteridium aquilinum or Pteridium esculentum (bracken), the fiddleheads used as a cooked vegetable in Japan and are believed to be responsible for the high rate of stomach cancer in Japan. It is also one of the world's most important agricultural weeds, especially in the British highlands, and often poisons cattle and horses.
• Diplazium esculentum (vegetable fern), a source of food for some native societies
• Pteris vittata (brake fern), used to absorb arsenic from the soil
• Polypodium glycyrrhiza (licorice fern), roots chewed for their pleasant flavor
• Tree ferns, used as building material in some tropical areas
• Cyathea cooperi (Australian tree fern), an important invasive species in Hawaii
• Ceratopteris richardii, a model plant for teaching and research, often called C-fern

Cultural connotations

Blätter des Manns Walfarn. by Alois Auer, Vienna: Imperial Printing Office, 1853

Ferns figure in folklore, for example in legends about mythical flowers or seeds.^[4] In Slavic folklore, ferns are believed to bloom once a year, during the Ivan Kupala night. Although alleged to be exceedingly difficult to find, anyone who sees a "fern flower" is thought to be guaranteed to be happy and rich for the rest of their life. Similarly, Finnish tradition holds that one who finds the "seed" of a fern in bloom on Midsummer night will, by possession of it, be able to travel invisibly and will be guided to the locations where eternally blazing Will o' the wisps called aarnivalkea, and which mark the spot of hidden treasure that is protected by a spell which prevents anyone else but the fern seed holder from ever accidentally stumbling in on the location of those caches^[5].

"Pteridomania"' is a term for the Victorian era craze of fern collecting and fern motifs in decorative art including pottery, glass, metals, textiles, wood, printed paper, and sculpture "appearing on everything from christening presents to gravestones and memorials." The fashion for growing ferns indoors led to the development of the Wardian case, a glazed cabinet that would exclude air pollutants and maintain the necessary humidity. ^[6]

Fractal fern created using chaos game, through an Iterated function system (IFS).

The dried form of ferns was also used in other arts, being used as a stencil or directly inked for use in a design. The botanical work, The Ferns of Great Britain and Ireland, is a notable example of this type of nature printing. The process, patented by the artist and publisher Henry Bradbury, impressed a specimen on to a soft lead plate. The first publication to demonstrate this was Alois Auer's The Discovery of the Nature Printing-Process.

Medicinal Value

Ferns are sometimes used in medicine to treat cuts and clean them out. Ferns are also good bandages if you are stuck out in the wild.^[7] Rubbing a sword fern frond spore-side-down on a stinging nettle sting removes the stinging. ^[8]

Misunderstood names

Several non-fern plants are called "ferns" and are sometimes confused with true ferns. These include:

• "Asparagus fern"—This may apply to one of several species of the monocot genus Asparagus, which are flowering plants.
• "Sweetfern"—A flowering shrub of the genus Comptonia.
• "Air fern"—A group of animals called hydrozoan that are distantly related to jellyfish and corals. They are harvested, dried, dyed green, and then sold as a "plant" that can "live on air". While it may look like a fern, it is merely the skeleton of this colonial animal.
• "Fern bush"—Chamaebatiaria millefolium—a rose family shrub with fern-like leaves.

In addition, the book Where the Red Fern Grows has elicited many questions about the mythical "red fern" named in the book. There is no such known plant, although there has been speculation that the oblique grape-fern, Sceptridium dissectum, could be referred to here, because it is known to appear on disturbed sites and its fronds may redden over the winter.

Gallery

Adiantum lunulatum	Fern leaf, probably Blechnum nudum	A tree fern unrolling a new frond	Tree fern, probably Dicksonia antarctica	Tree ferns, probably Dicksonia antarctica
"Filicinae" from Ernst Haeckel's Kunstformen der Natur, 1904	Unidentified tree fern in Oaxaca	Tree Fern Spores San Diego, CA	Leaf of fern	Unidentified fern with spores showing in Rotorua, NZ.
Ferns in one of many natural Coast Redwood undergrowth settings Santa Cruz, CA.	Nature prints in The Ferns of Great Britain and Ireland used fronds to produce the plates	A young, newly-formed fern frond	Fern fronds.