FERN

Fern
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This article is about the family of pteridophyte plants. For the environmental organisation, see FERN (NGO). For the
letter of the Ogham alphabet, see Fern (letter).
Ferns (Pteridophyta)

Fossil range: Late Devonian - Recent

Polystichum setiferum showing unrolling young frond
Scientific classification
Kingdom: Plantae

Division: Pteridophyta

Classes
Psilotopsida
Equisetopsida
Marattiopsida
Pteridopsida (Polypodiopsida)

A fern is any one of a group of about 20,000 species of plants classified in the phylum or division Pteridophyta, also
known as Filicophyta. The group is also referred to as polypodiophyta, or polypodiopsida when treated as a subdivision
of tracheophyta (vascular plants). The study of ferns is called pteridology; one who studies ferns is called a
pteridologist. The term pteridophytes has traditionally been used to describe all seedless vascular plants so is
synonymous with "ferns and fern allies". This can be confusing given that the fern phylum Pteridophyta is also
sometimes referred to as pteridophytes.

A fern is a vascular plant that differs from the more primitive lycophytes in having true leaves (megaphylls), and from
the more advanced seed plants (gymnosperms and angiosperms) in lacking seeds. Like all vascular plants, it has a life
cycle, often referred to as alternation of generations, characterized by a diploid sporophytic and a haploid gametophytic
phase. Unlike the gymnosperms and angiosperms, in ferns the gametophyte is a free-living organism. The life cycle of a
typical fern is as follows:

A sporophyte (diploid) phase produces haploid spores by meiosis;
A spore grows by cell division into a gametophyte, which typically consists of a photosynthetic prothallus
The gametophyte produces gametes (often both sperm and eggs on the same prothallus) by mitosis
A mobile, flagellate sperm fertilizes an egg that remains attached to the prothallus
The fertilized egg is now a diploid zygote and grows by mitosis into a sporophyte (the typical "fern" plant).
Contents [hide]
1 Fern ecology
2 Fern structure
3 Evolution and classification
4 Economic uses
5 Cultural connotations
6 Misunderstood names
7 Gallery
8 References
9 See also
10 External links

[edit] Fern ecology
Ferns have a popular image of growing in moist, shady woodland nooks, but the reality is far more complex. Ferns grow
in a wide variety of habitats, ranging from remote mountain elevations to dry desert rock faces to bodies of water to
open fields. Ferns in general may be thought of as largely being specialists in marginal habitats, often succeeding in
places where various environmental delimiters limit the success of flowering plants. On the other hand, some ferns are
among the world's most serious weed species, such as the bracken growing in the British highlands, or the mosquito
fern (Azolla) growing in tropical lakes. There are four particular types of habitats that are often key places to find ferns:
the afore-mentioned moist, shady forest cove; the sheltered rock face, especially when sheltered from the full sun; acid
bogs and swamps; and tropical trees, where many species are epiphytes.

Many ferns depend on associations with mycorrhizal fungi. Many ferns only grow within specific pH ranges; for instance,
the climbing fern (Lygodium) of eastern North America will only grow in moist, intensely acid soils, while the bulblet
bladder fern (Cystopteris bulbifera) with overlapping range is only ever found on limestone

[edit] Fern structure

Ferns at the Royal Melbourne Botanical Gardens
Tree ferns, probably Dicksonia antarcticaLike the sporophytes of seed plants, those of ferns consist of:

Stems: Most often an underground creeping rhizome, but sometimes an above-ground creeping stolon (e.g.,
Polypodiaceae), or an above-ground erect semi-woody trunk (e.g., Cyatheaceae) reaching up to 20 m in a few species
(e.g., Cyathea brownii on Norfolk Island and Cyathea medullaris in New Zealand).
Leaf: The green, photosynthetic part of the plant. In ferns, it is often referred to as a frond, but this is because of the
historical division between people who study ferns and people who study seed plants, rather than because of
differences in structure. New leaves typically expand by the unrolling of a tight spiral called a crozier or fiddlehead. This
uncurling of the leaf is termed circinate vernation. Leaves are divided into two types:
Trophophyll: A leaf that does not produce spores, instead only producing sugars by photosynthesis. Analogous to the
typical green leaves of seed plants.
Sporophyll: A leaf that produces spores. These leaves are analogous to the scales of pine cones or to stamens and
pistil in gymnosperms and angiosperms, respectively. Unlike the seed plants, however, the sporophylls of ferns are
typically not very specialized, looking similar to trophophylls and producing sugars by photosynthesis as the
trophophylls do.
Roots: The underground non-photosynthetic structures that take up water and nutrients from soil. They are always
fibrous and are structurally very similar to the roots of seed plants.
The gametophytes of ferns, however, are very different from those of seed plants. They typically consist of:

Prothallus: A green, photosynthetic structure that is one cell thick, usually heart- or kidney-shaped, 3-10 mm long and
2-8 mm broad. The thallus produces gametes by means of:
Antheridia: Small spherical structures that produce flagellate sperm.
Archegonia: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming
down the neck.
Rhizoids: root-like structures (not true roots) that consist of single greatly-elongated cells, water and mineral salts are
absorbed over the whole structure. Rhizoids anchor the prothallus to the soil.

[edit] Evolution and classification
Ferns first appear in the fossil record in the early-Carboniferous period. By the Triassic, the first evidence of ferns
related to several modern families appeared. The "great fern radiation" occurred in the late-Cretaceous, when many
modern families of ferns first appeared.

Ferns have traditionally been grouped in the Class Filices, but modern classifications assign them their own division in
the plant kingdom, called Pteridophyta.

Traditionally, three discrete groups of plants have been considered ferns: two groups of eusporangiate ferns--families
Ophioglossaceae (adders-tongues, moonworts, and grape-ferns) and Marattiaceae--and the leptosporangiate ferns.
The Marattiaceae are a primitive group of tropical ferns with a large, fleshy rhizome, and are now thought to be a sibling
taxon to the main group of ferns, the leptosporangiate ferns. Several other groups of plants were considered "fern
allies": the clubmosses, spikemosses, and quillworts in the Lycopodiophyta, the whisk ferns in Psilotaceae, and the
horsetails in the Equisetaceae. More recent genetic studies have shown that the Lycopodiophyta are only distantly
related to any other vascular plants, having radiated evolutionarily at the base of the vascular plant clade, while both
the whisk ferns and horsetails are as much "true" ferns as are the Ophioglossoids and Marattiaceae. In fact, the whisk
ferns and Ophioglossoids are demonstrably a clade, and the horsetails and Marattiaceae are arguably another clade.

One possible means of treating this situation is to consider only the leptosporangiate ferns as "true" ferns, while
considering the other three groups as "fern allies". In practice, numerous classification schemes have been proposed
for ferns and fern allies, and there has been little consensus among them. A new classification by Smith et al. (2006) is
based on recent molecular systematic studies, in addition to morphological data. This classification divides ferns into
four classes:

Psilotopsida
Equisetopsida
Marattiopsida
Polypodiopsida
The last group includes most plants familiarly known as ferns. Modern research supports older ideas based on
morphology that the Osmundaceae diverged early in the evolutionary history of the leptosporangiate ferns; in certain
ways this family is intermediate between the eusporangiate ferns and the leptosporangiate ferns.

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
Family Lindsaeaceae (incl. Cystodiaceae, Lonchitidaceae)
Family Saccolomataceae
Family Dennstaedtiaceae (incl. Hypolepidaceae, Monachosoraceae, Pteridiaceae)
Family Pteridaceae (incl. Acrostichaceae, Actiniopteridaceae, Adiantaceae, Anopteraceae, Antrophyaceae,
Ceratopteridaceae, Cheilanthaceae, Cryptogrammaceae, Hemionitidaceae, Negripteridaceae, Parkeriaceae,
Platyzomataceae, Sinopteridaceae, Taenitidaceae, Vittariaceae)
Family Aspleniaceae
Family Thelypteridaceae
Family Woodsiaceae (incl. Athyriaceae, Cystopteridaceae)
Family Blechnaceae (incl. Stenochlaenaceae)
Family Onocleaceae
Family Dryopteridaceae (incl. Aspidiaceae, Bolbitidaceae, Elaphoglossaceae, Hypodematiaceae, Peranemataceae)
Family Lomariopsidaceae (incl. Nephrolepidaceae)
Family Tectariaceae
Family Oleandraceae
Family Davalliaceae
Family Polypodiaceae (incl. Drynariaceae, Grammitidaceae, Gymnogrammitidaceae, Loxogrammaceae, Platyceriaceae,
Pleurisoriopsidaceae)

[edit] 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 birds-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.

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 (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

[edit] Cultural connotations
In Slavic folklore, ferns are believed to bloom once a year, during the Ivan Kupala night. Although it's exceedingly
difficult to find, anyone who takes a look of a fern-flower will be happy and rich for the rest of his life. Similarly in
Finland, the tradition holds that one who finds the seed of a fern in bloom on Midsummer night, will by the possession of
it be able to travel under a glamour of invisibility and shall be guided to the locations where eternally blazing Will o' the
wisps mark the spot of hidden treasure caches.

[edit] Misunderstood names
Several non-fern plants are called "ferns" and are sometimes popularly believed to be ferns in error. These include:

"Asparagus fern" - This may apply to one of several species of the monocot genus Asparagus, which are flowering
plants. A better name would be "fern asparagus".
"Sweetfern" - This is a shrub of the genus Comptonia.
"Air fern" - This not a plant at all but an animal, a hydrozoan, and distantly related to jellyfish and corals. It is 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.
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.

[edit] Gallery
Wikimedia Commons has media related to:
Pteridophyta
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.

[edit] References
Pryer, Kathleen M., Harald Schneider, Alan R. Smith, Raymond Cranfill, Paul G. Wolf, Jeffrey S. Hunt and Sedonia D.
Sipes. 2001. Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants. Nature 409:
618-622 (abstract here).
Pryer, Kathleen M., Eric Schuettpelz, Paul G. Wolf, Harald Schneider, Alan R. Smith and Raymond Cranfill. 2004.
Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences. American
Journal of Botany 91:1582-1598 (online abstract here).
Moran, Robbin C. (2004). A Natural History of Ferns. Portland, OR: Timber Press. ISBN 0-88192-667-1.
Lord, Thomas R. (2006). Ferns and Fern Allies of Pennsylvania. Indiana, PA: Pinelands Press. [1]
Smith, A. R., K. M. Pryer, E. Schuettpelz, P. Korall, H. Schneider & P. G. Wolf. 2006. A classification for extant ferns.
Taxon 55(3):705–731.

[edit] See also
Fern spike

[edit] External links
Tree of Life Web Project: Filicopsida
A classification of the ferns and their allies
A fern book bibliography
Register of fossil Pteridophyta
L. Watson and M.J. Dallwitz (2004 onwards). The Ferns (Filicopsida) of the British Isles.
Non-seed plant images at bioimages.vanderbilt.edu
Retrieved from "http://en.wikipedia.org/wiki/Fern"
Categories: Pteridophyta | Botany | Gardening | Horticulture | Invisibility
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