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{{dablink|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)]]. }}
{{Taxobox
| color = lightgreen
| name = Ferns (Pteridophyta)
| fossil_range = [[Early Carboniferous]] - Recent
| image = Polystichum_setiferum0.jpg
| image_width = 240px
| image_caption = ''[[Polystichum setiferum]]'' showing unrolling young frond
| regnum = [[Plant]]ae
| divisio = '''Pteridophyta'''
| subdivision_ranks = Classes
| subdivision =
[[Psilotopsida]]<br>
[[Equisetopsida]]<br>
[[Marattiopsida]]<br>
[[Polypodiopsida]]
}}
A '''fern''' is any one of a group of about 20,000 [[species]] of [[plant]]s 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 [[pteridophyte]]s has traditionally been used to describe all seedless [[vascular plant]]s 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 [[lycophyte]]s in having true [[leaf|leaves]] (megaphylls), and from the more advanced [[seed plant]]s ([[gymnosperm]]s and [[angiosperm]]s) in lacking [[seed]]s. Like all vascular plants, it has a [[biological life cycle|life cycle]], often referred to as [[alternation of generations]], characterised by a [[diploid]] [[sporophyte|sporophytic]] and a [[haploid]] [[gametophyte|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]] [[spore]]s 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 [[Ovum|egg]]s on the same prothallus) by [[mitosis]]
# A mobile, [[flagellum|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).
==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 [[habitat]]s, 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 plant]]s. 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 [[bog]]s and [[swamp]]s; and tropical [[tree]]s, where many species are [[epiphyte]]s.
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]]
== Fern structure ==
[[Image:Ferns at melb botanical gardens.jpg|thumb|Ferns at the Royal Melbourne Botanical Gardens]]
[[Image:Ferns02.jpg|thumb|Tree ferns, probably ''Dicksonia antarctica'']]
Like the sporophytes of seed plants, those of ferns consist of:
* [[Plant stem|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]], [[photosynthesis|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.
* [[Root]]s: The underground non-photosynthetic structures that take up water and nutrients from soil. They are always [[fibrous root system|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:
** [[antheridium|Antheridia]]: Small spherical structures that produce [[flagellum|flagellate]] sperm.
** [[archegonium|Archegonia]]: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck.
* [[Rhizoid]]s: [[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.
==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]] ([[Ophioglossum|adders-tongues]], [[moonwort]]s, and [[grape-fern]]s) and [[Marattiaceae]]--and the [[sporangium|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 ally|fern allies]]": the [[clubmoss]]es, [[spikemoss]]es, and [[quillwort]]s in the [[Lycopodiophyta]], the [[whisk fern]]s in [[Psilotaceae]], and the [[horsetail]]s in the [[Equisetaceae]]. More recent genetic studies have shown that the Lycopodiophyta are only distantly related to any other [[vascular plant]]s, 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 "fe
rn 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.
A more complete classification scheme (with alternative names in brackets) follows:
*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 [[Polypodiopsida]] [=Filicopsida]
**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]])
==Economic uses==
Ferns are not as important economically as seed plants but have considerable importance. Ferns of the genus ''[[mosquito fern|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 [[nitrogen fixation|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 [[greenery|cut foliage]] and as [[houseplant]]s, especially the [[Boston fern]] (''Nephrolepis exaltata''). Several ferns are noxio
us [[weed]]s 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]]
*''[[Rumohra adiantoides]]'' (floral fern), extensively used in the [[floristry|florist]] trade
*''[[Osmunda|Osmunda regalis]]'' (royal fern) and ''[[Osmunda|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
*''[[Diplazium esculentum]]'' (vegetable fern), a source of food for some native societies
*''[[Pteris|Pteris vittata]]'' (brake fern), used to absorb [[arsenic]] from the soil
*''Polypodium glycyrrhiza'' (licorice fern), roots chewed for their pleasant flavor
*[[Tree fern]]s, used as building material in some tropical areas
*[[Bracken]] fern, often poisons cattle and horses
*''[[Cyathea cooperi]]'' (Australian tree fern), an important invasive species in Hawaii
*''[[Dryopteris filix-mas]]'', this fern accidentally sprouting in a bottle resulted in Nathaniel Bagshaw Ward's 1829 invention of the terrarium or [[Wardian case]]
*[[Parkeriaceae|''Ceratopteris'']] ''richardii'', a model plant for teaching and research, often called C-fern
==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 wisp]]s mark the spot of hidden [[treasure]] caches.
==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 [[monocotyledon|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 is an unrelated aquatic animal that is related to a coral; it is harvested, dried, dyed green, then sold as plant that can "live on air". It looks like a fern but is actually a skeleton.
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|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 ==
{{Commonscat|Pteridophyta}}
<gallery>
Image:Fern.jpg|Fern leaf, probably ''Blechnum nudum''
Image:Tree Fern.jpg|A tree fern unrolling a new frond
Image:Fern02.jpg|Tree fern, probably ''Dicksonia antarctica''
Image:Ferns.jpg|Tree ferns, probably ''Dicksonia antarctica''
Image:Haeckel Filicinae 92.jpg|"Filicinae" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904
Image:Oaxaca fern.jpg|Unidentified tree fern in [[Oaxaca (state)|Oaxaca]]
Image:Tree Fern Spores.jpg|Tree Fern Spores [[San Diego, CA]]
Image:Fern-leaf-oliv.jpg|Leaf of fern
Image:Fern leaves.jpg|Unidentified fern with spores showing in [[Rotorua]], [[New Zealand|NZ]].
Image:CowellFerns.JPG|Ferns in a natural
[[Sequoia|Coast Redwood]] undergrowth setting [[Santa Cruz, CA]].
</gallery>
{{-}}
==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 [http://www.nature.com/nature/journal/v409/n6820/abs/409618a0.html 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 [http://www.amjbot.org/cgi/content/abstract/91/10/1582 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. [http://www.paferns.com]
* 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.
==See also==
* [[Fern spike]]
==External links==
* [http://ontarioferns.com Ontario Ferns]
* [http://tolweb.org/tree?group=Filicopsida&contgroup=Embryophytes Tree of Life Web Project: Filicopsida]
* A classification of the [http://www.anbg.gov.au/fern/taxa/classification.html ferns and their allies]
* [http://www.jaknouse.athens.oh.us/ferns/bookfern.html A fern book bibliography]
* [http://www1.akira.ne.jp/~unzen/pteridophyta.html Register of fossil Pteridophyta]
* [http://delta-intkey.com/britfe/ L. Watson and M.J. Dallwitz (2004 onwards). The Ferns (Filicopsida) of the British Isles.]
* [http://www.cas.vanderbilt.edu/bioimages/pages/non-seed-plants.htm Non-seed plant images at bioimages.vanderbilt.edu]
[[Category:Pteridophyta| ]]
[[Category:Botany]]
[[Category:Gardening]]
[[Category:Horticulture]]
{{Taxobox
| color = lightgreen
| name = Ferns (Pteridophyta)
| fossil_range = [[Early Carboniferous]] - Recent
| image = Polystichum_setiferum0.jpg
| image_width = 240px
| image_caption = ''[[Polystichum setiferum]]'' showing unrolling young frond
| regnum = [[Plant]]ae
| divisio = '''Pteridophyta'''
| subdivision_ranks = Classes
| subdivision =
[[Psilotopsida]]<br>
[[Equisetopsida]]<br>
[[Marattiopsida]]<br>
[[Polypodiopsida]]
}}
A '''fern''' is any one of a group of about 20,000 [[species]] of [[plant]]s 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 [[pteridophyte]]s has traditionally been used to describe all seedless [[vascular plant]]s 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 [[lycophyte]]s in having true [[leaf|leaves]] (megaphylls), and from the more advanced [[seed plant]]s ([[gymnosperm]]s and [[angiosperm]]s) in lacking [[seed]]s. Like all vascular plants, it has a [[biological life cycle|life cycle]], often referred to as [[alternation of generations]], characterised by a [[diploid]] [[sporophyte|sporophytic]] and a [[haploid]] [[gametophyte|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]] [[spore]]s 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 [[Ovum|egg]]s on the same prothallus) by [[mitosis]]
# A mobile, [[flagellum|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).
==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 [[habitat]]s, 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 plant]]s. 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 [[bog]]s and [[swamp]]s; and tropical [[tree]]s, where many species are [[epiphyte]]s.
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]]
== Fern structure ==
[[Image:Ferns at melb botanical gardens.jpg|thumb|Ferns at the Royal Melbourne Botanical Gardens]]
[[Image:Ferns02.jpg|thumb|Tree ferns, probably ''Dicksonia antarctica'']]
Like the sporophytes of seed plants, those of ferns consist of:
* [[Plant stem|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]], [[photosynthesis|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.
* [[Root]]s: The underground non-photosynthetic structures that take up water and nutrients from soil. They are always [[fibrous root system|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:
** [[antheridium|Antheridia]]: Small spherical structures that produce [[flagellum|flagellate]] sperm.
** [[archegonium|Archegonia]]: A flask-shaped structure that produces a single egg at the bottom, reached by the sperm by swimming down the neck.
* [[Rhizoid]]s: [[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.
==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]] ([[Ophioglossum|adders-tongues]], [[moonwort]]s, and [[grape-fern]]s) and [[Marattiaceae]]--and the [[sporangium|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 ally|fern allies]]": the [[clubmoss]]es, [[spikemoss]]es, and [[quillwort]]s in the [[Lycopodiophyta]], the [[whisk fern]]s in [[Psilotaceae]], and the [[horsetail]]s in the [[Equisetaceae]]. More recent genetic studies have shown that the Lycopodiophyta are only distantly related to any other [[vascular plant]]s, 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 "fe
rn 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.
A more complete classification scheme (with alternative names in brackets) follows:
*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 [[Polypodiopsida]] [=Filicopsida]
**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]])
==Economic uses==
Ferns are not as important economically as seed plants but have considerable importance. Ferns of the genus ''[[mosquito fern|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 [[nitrogen fixation|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 [[greenery|cut foliage]] and as [[houseplant]]s, especially the [[Boston fern]] (''Nephrolepis exaltata''). Several ferns are noxio
us [[weed]]s 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]]
*''[[Rumohra adiantoides]]'' (floral fern), extensively used in the [[floristry|florist]] trade
*''[[Osmunda|Osmunda regalis]]'' (royal fern) and ''[[Osmunda|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
*''[[Diplazium esculentum]]'' (vegetable fern), a source of food for some native societies
*''[[Pteris|Pteris vittata]]'' (brake fern), used to absorb [[arsenic]] from the soil
*''Polypodium glycyrrhiza'' (licorice fern), roots chewed for their pleasant flavor
*[[Tree fern]]s, used as building material in some tropical areas
*[[Bracken]] fern, often poisons cattle and horses
*''[[Cyathea cooperi]]'' (Australian tree fern), an important invasive species in Hawaii
*''[[Dryopteris filix-mas]]'', this fern accidentally sprouting in a bottle resulted in Nathaniel Bagshaw Ward's 1829 invention of the terrarium or [[Wardian case]]
*[[Parkeriaceae|''Ceratopteris'']] ''richardii'', a model plant for teaching and research, often called C-fern
==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 wisp]]s mark the spot of hidden [[treasure]] caches.
==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 [[monocotyledon|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 is an unrelated aquatic animal that is related to a coral; it is harvested, dried, dyed green, then sold as plant that can "live on air". It looks like a fern but is actually a skeleton.
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|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 ==
{{Commonscat|Pteridophyta}}
<gallery>
Image:Fern.jpg|Fern leaf, probably ''Blechnum nudum''
Image:Tree Fern.jpg|A tree fern unrolling a new frond
Image:Fern02.jpg|Tree fern, probably ''Dicksonia antarctica''
Image:Ferns.jpg|Tree ferns, probably ''Dicksonia antarctica''
Image:Haeckel Filicinae 92.jpg|"Filicinae" from [[Ernst Haeckel]]'s ''[[Kunstformen der Natur]]'', 1904
Image:Oaxaca fern.jpg|Unidentified tree fern in [[Oaxaca (state)|Oaxaca]]
Image:Tree Fern Spores.jpg|Tree Fern Spores [[San Diego, CA]]
Image:Fern-leaf-oliv.jpg|Leaf of fern
Image:Fern leaves.jpg|Unidentified fern with spores showing in [[Rotorua]], [[New Zealand|NZ]].
Image:CowellFerns.JPG|Ferns in a natural
[[Sequoia|Coast Redwood]] undergrowth setting [[Santa Cruz, CA]].
</gallery>
{{-}}
==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 [http://www.nature.com/nature/journal/v409/n6820/abs/409618a0.html 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 [http://www.amjbot.org/cgi/content/abstract/91/10/1582 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. [http://www.paferns.com]
* 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.
==See also==
* [[Fern spike]]
==External links==
* [http://ontarioferns.com Ontario Ferns]
* [http://tolweb.org/tree?group=Filicopsida&contgroup=Embryophytes Tree of Life Web Project: Filicopsida]
* A classification of the [http://www.anbg.gov.au/fern/taxa/classification.html ferns and their allies]
* [http://www.jaknouse.athens.oh.us/ferns/bookfern.html A fern book bibliography]
* [http://www1.akira.ne.jp/~unzen/pteridophyta.html Register of fossil Pteridophyta]
* [http://delta-intkey.com/britfe/ L. Watson and M.J. Dallwitz (2004 onwards). The Ferns (Filicopsida) of the British Isles.]
* [http://www.cas.vanderbilt.edu/bioimages/pages/non-seed-plants.htm Non-seed plant images at bioimages.vanderbilt.edu]
[[Category:Pteridophyta| ]]
[[Category:Botany]]
[[Category:Gardening]]
[[Category:Horticulture]]
