View source for Fern

{{Short description|Class of vascular plants }}
{{About|a group of plants||Fern (disambiguation)|and|Ferns (disambiguation)}}
{{More citations needed|date=August 2023}}
{{Use dmy dates|date=June 2017}}
{{Automatic taxobox
| name           = Ferns
| fossil_range   = {{Fossil range|Late Devonian|0|Middle [[Devonian]]{{sfn|Stein et al|2007}} – [[Holocene|Present]]}}
|image={{Multiple image
|perrow          = 2
|total_width     = 270
|image1          = Psilotum.jpg
|caption1        = [[Psilotales]]
|image2          = Equisetopsida.jpg
|caption2        = [[Equisetales]] 
|image3          = Flickr - brewbooks - Angiopteris evecta - Mule's foot fern (1).jpg
|caption3        = [[Marattiales]]
|image4          = Osmunda regalis Moore50.png
|caption4        = [[Osmundales]]
|image5          = WP2-Hymenophyllum-Exkursion nach Berdorf (Luxemburgexkursion) 011.jpg
|caption5        = [[Hymenophyllales]]
|image6          = Dipteris conjugata 破傘蕨 001 (天問).jpg
|caption6        = [[Gleicheniales]]
|image7          = Tree Fern (48717210587).jpg
|caption7        = [[Cyatheales]]
|image8          = The ferns of Great Britain, and their allies the club-mosses, pepperworts, and horsetails (Pl. 2) (8515393495).jpg
|caption8        = [[Polypodiales]]
|border          = infobox
}}
| taxon = Polypodiopsida
| authority = Cronquist, Takht. & W.Zimm.
| subdivision_ranks = Subclasses{{sfn|Pteridophyte Phylogeny Group|2016}}
| subdivision =
* †[[Stauropterididae]]
* †[[Zygopterididae]]
* [[Equisetidae]]
* [[Marattiidae]]
* [[Ophioglossidae]]
* [[Polypodiidae (plant)|Polypodiidae]]
| synonyms =
* Filicatae <small>Kubitski 1990</small>
* Filices
* Filicophyta <small>Endlicher 1836</small>
* Monilophyta <small>Cantino & Donoghue 2007</small>
* Pteridopsida <small>Ritgen 1828</small>
}}

The '''ferns''' ('''Polypodiopsida''' or '''Polypodiophyta''') are a group of [[vascular plant]]s (plants with [[xylem]] and [[phloem]]) that reproduce via [[spore]]s and have neither [[seed]]s nor [[flower]]s. They differ from [[moss]]es by being vascular, i.e., having specialized tissues that conduct water and nutrients, and in having life cycles in which the branched [[sporophyte]] is the dominant phase.<ref name=":0">{{Cite book |title=The Ultimate Family Visual Dictionary |publisher=[[DK Pub.]] |year=2012 |isbn=978-0-1434-1954-9 |location=New Delhi |pages=118-121 |language=en}}</ref>

Ferns have complex [[leaf|leaves]] called [[megaphyll]]s that are more complex than the [[microphyll]]s of [[clubmosses]]. Most ferns are [[leptosporangiate fern]]s. They produce coiled [[Fiddlehead fern|fiddleheads]] that uncoil and expand into [[frond]]s. The group includes about 10,560 known extant species. Ferns are defined here in the broad sense, being all of the [[Polypodiopsida]], comprising both the leptosporangiate ([[Polypodiidae (plant)|Polypodiidae]]) and [[eusporangiate fern]]s, the latter group including [[horsetail]]s, [[Psilotaceae|whisk ferns]], [[marattioid fern]]s, and [[ophioglossoid fern]]s.

The fern [[crown group]], consisting of the leptosporangiates and eusporangiates, is estimated to have originated in the late [[Silurian]] period 423.2 million years ago,<ref name="Polypodiopsida">{{cite journal |last1=Nitta |first1=Joel H. |last2=Schuettpelz |first2=Eric |last3=Ramírez-Barahona |first3=Santiago |last4=Iwasaki |first4=Wataru |display-authors=et al. |year=2022 |title=An Open and Continuously Updated Fern Tree of Life |journal=Frontiers in Plant Science |volume=13 |page=909768 |doi=10.3389/fpls.2022.909768 |pmid=36092417 |pmc=9449725 |doi-access=free}}</ref> but [[Polypodiales]], the group that makes up 80% of living fern diversity, did not appear and diversify until the [[Cretaceous]], contemporaneous with the rise of flowering plants that came to dominate the world's flora.

Ferns are not of major economic importance, but some are used for food, medicine, as [[biofertilizer]], as ornamental plants, and for remediating contaminated soil. They have been the subject of research for their ability to remove some chemical pollutants from the atmosphere. Some fern species, such as bracken (''[[Pteridium aquilinum]]'') and water fern (''[[Azolla filiculoides]]''), are significant weeds worldwide. Some fern genera, such as ''[[Azolla]]'', can [[nitrogen fixation|fix nitrogen]] and make a significant input to the nitrogen nutrition of [[Paddy field|rice paddies]]. They also play certain roles in folklore.

==Description==

=== Sporophyte ===

Extant ferns are herbaceous [[Perennial plant|perennials]] and most lack [[wood]]y growth.<ref>{{Cite book |last=Mauseth |first=James D. |url=https://books.google.com/books?id=UEsBPPlxP7EC&pg=PA492 |title=Botany: an Introduction to Plant Biology |date=September 2008 |publisher=Jones & Bartlett Publishers |isbn=978-1-4496-4720-9 |page=492}}</ref> When woody growth is present, it is found in the stem.<ref name="Levyns-1966">{{Cite book |last=Levyns |first=M. R. |title=A Guide to the Flora of the Cape Peninsula |publisher=Juta & Company |year=1966 |edition=2nd Revised |oclc=621340}}</ref> Their foliage may be [[deciduous]] or [[evergreen]],<ref>{{Cite book |last1=Fernández |first1=Helena |url=https://books.google.com/books?id=smtpBM7UgXEC&pg=PA175 |title=Working with Ferns: Issues and Applications |last2=Kumar |first2=Ashwani |last3=Revilla |first3=Maria Angeles |date=2010-11-11 |publisher=Springer |isbn=978-1-4419-7162-3 |page=175}}</ref> and some are semi-evergreen depending on the climate.<ref>{{Cite book |last=Hodgson |first=Larry |url=https://books.google.com/books?id=HDij6Fmk2MwC&pg=PA329 |title=Making the Most of Shade: How to Plan, Plant, and Grow a Fabulous Garden that Lightens Up the Shadows |date=2005-01-01 |publisher=Rodale |isbn=978-1-57954-966-4 |page=329}}</ref> Like the sporophytes of seed plants, those of ferns consist of stems, leaves and roots. Ferns differ from [[spermatophyte]]s in that they reproduce by spores rather than having flowers and producing seeds.<ref name="Levyns-1966" /> However, they also differ from spore-producing [[bryophyte]]s in that, like seed plants, they are [[polysporangiophyte]]s, their [[sporophyte]]s branching and producing many sporangia. Also unlike bryophytes, fern sporophytes are free-living and only briefly dependent on the maternal [[gametophyte]].

The [[green]], [[photosynthesis|photosynthetic]] part of the plant is technically a [[microphyll#evolution of leaves: microphyll and megaphyll|megaphyll]] and in ferns, it is often called a ''[[frond]]''. New leaves typically expand by the unrolling of a tight spiral called a crozier or [[fiddlehead fern|fiddlehead]] into [[frond]]s.{{sfn|McCausland|2019}} This uncurling of the leaf is termed [[circinate vernation]]. Leaves are divided into two types: sporophylls and tropophylls. [[Sporophyll]]s produce spores; [[tropophyll]]s do not. Fern spores are borne in [[sporangia]] which are usually clustered to form [[sorus|sori]]. The sporangia may be covered with a protective coating called an [[indusium]]. The arrangement of the sporangia is important in classification.<ref name="Levyns-1966" />

In monomorphic ferns, the fertile and sterile leaves look morphologically the same, and both are able to photosynthesize. In hemidimorphic ferns, just a portion of the fertile leaf is different from the sterile leaves. In dimorphic (holomorphic) ferns, the two types of leaves are [[frond dimorphism|morphologically distinct]].<ref>[https://2019.botanyconference.org/engine/search/index.php?func=detail&aid=758 Understanding the contribution of LFY and PEBP flowering genes to fern leaf dimorphism – Botany 2019].</ref> The fertile leaves are much narrower than the sterile leaves, and may have no green tissue at all, as in the [[Blechnaceae]] and [[Lomariopsidaceae]].

[[File:Croziers, fronds, rhizomes of bracken fern.jpg|thumb|Croziers, fronds, and [[rhizome]]s of bracken. In this species the stems grow underground, allowing the plant to spread horizontally.]]

The anatomy of fern leaves can be anywhere from simple to highly divided, or even [[Indeterminate growth|indeterminate]] (e.g. [[Gleicheniaceae]], [[Lygodium|Lygodiaceae]]). The divided forms are [[Pinnation|pinnate]], where the leaf segments are completely separated from one other, or pinnatifid (partially pinnate), where the leaf segments are still partially connected. When the fronds are branched more than once, it can also be a combination of the pinnatifid are pinnate shapes. If the leaf blades are divided twice, the plant has bipinnate fronds, and tripinnate fronds if they branch three times, and all the way to tetra- and pentapinnate fronds.<ref>[https://www.fs.fed.us/wildflowers/beauty/ferns/structure.shtml Fern Structure – Forest Service].</ref><ref>[https://www.nzplants.auckland.ac.nz/en/about/ferns/structure/frond.html Fern Structure – Forest Service], Auckland, New Zealand.</ref> In tree ferns, the main stalk that connects the leaf to the stem (known as the stipe), often has multiple leaflets. The leafy structures that grow from the stipe are known as pinnae and are often again divided into smaller pinnules.<ref>{{cite web |url=http://www.basicbiology.net/plants/ferns/fronds.php |title=Fern Fronds |publisher=Basic Biology |access-date=2014-12-06 |archive-date=19 April 2015 |archive-url=https://web.archive.org/web/20150419003216/http://basicbiology.net/plants/ferns/fronds.php |url-status=dead}}</ref>

Fern stems are often loosely called [[rhizome]]s, even though they grow underground only in some of the species. Epiphytic species and many of the terrestrial ones have above-ground creeping [[stolon]]s (e.g., [[Polypodiaceae]]), and many groups have above-ground erect semi-woody trunks (e.g., [[Cyatheaceae]], the scaly tree ferns). These can reach up to {{convert|20|m|ft|sp=us}} tall in a few species (e.g., ''[[Cyathea brownii]]'' on [[Norfolk Island]] and ''[[Cyathea medullaris]]'' in [[New Zealand]]).<ref>{{cite book |first1=Mark F. |last1=Large |first2=John E. |last2=Braggins |author-link2=John E. Braggins |date=2004 |title=Tree Ferns |publisher=Timber Press |isbn=0881926302 |url-access=registration |url=https://archive.org/details/treeferns00mark |page= }}</ref>

Roots are 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.

=== Gametophyte ===

As in all [[vascular plant]]s, the sporophyte is the dominant phase or [[alternation of generations|generation in the life cycle]]. The [[gametophyte]]s of ferns, however, are very different from those of seed plants. They are free-living and resemble [[liverworts]], whereas those of seed plants develop within the spore wall and are dependent on the parent sporophyte for their nutrition. A fern gametophyte typically consists of:<ref name=":0" />

* [[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 prothallus produces gametes by means of:
** [[Antheridium|Antheridia]]: Small spherical structures that produce [[flagellum|flagellate]] antherozoids.<ref name=":0" />
** [[Archegonium|Archegonia]]: A flask-shaped structure that produces a single egg at the bottom, reached by the male gametophyte by swimming down the neck.<ref name=":0" />
* [[Rhizoid]]s: [[root]]-like structures (not true roots) that consist of single greatly elongated cells, that absorb water and mineral [[salts]] over the whole structure. Rhizoids anchor the prothallus to the soil.<ref name=":0" />

== Life cycle and reproduction ==
[[File:Onoclea sensibilis 4 crop.jpg|thumb|New fern (''[[Onoclea sensibilis]]'') emerges from the [[prothallus]].]]
The lifecycle of a fern involves two stages, as in [[Lycopodiopsida|club mosses]] and [[Equisetum|horsetails]]. In stage one, the spores are produced by [[Sporophyte|sporophytes]] in [[Sporangium|sporangia]], which are clustered together in sori (''s.g. sorus''), developing on the underside of fertile fronds. In stage two, the spores germinate into a short-lived structure anchored to the ground by rhizoids called [[gametophyte]] which produce gametes. When a mature fertile frond bears sori, and spores are released, the spores will settle on the soil and send out [[Rhizoid|rhizoids]], while it develops into a [[prothallus]]. The prothallus bears spherical [[Antheridium|antheridia]] (''s.g. antheridium'') which produce antherozoids (male gametophytes) and [[Archegonium|archegonia]] (''s.g. archegonium'') which release a single [[Egg cell|oosphere]]. The antherozoid swims up the archegonium and fertilize the oosphere, resulting in a zygote, which will grow into a separate sporophyte, while the gametophyte shortly persists as a free-living plant.<ref name=":0" />

== Taxonomy ==

[[Carl Linnaeus]] (1753) originally recognized 15 genera of ferns and fern allies, classifying them in class [[Cryptogamia]] in two groups, Filices (e.g. ''[[Polypodium]]'') and [[Musci]] (mosses).{{sfn|Underwood|1903}}{{sfn|Linnaeus|1753}}{{sfn|Schuettpelz et al|2018}} By 1806 this had increased to 38 genera,{{sfn|Swartz|1806}} and has progressively increased since (''see {{harvtxt|Schuettpelz et al|2018}}''). Ferns were traditionally classified in the [[class (biology)|class]] Filices, and later in a [[phylum|Division]] of the Plant Kingdom named [[Pteridophyta]] or Filicophyta. Pteridophyta is no longer recognised as a valid [[taxon]] because it is [[paraphyletic]]. The ferns are also referred to as Polypodiophyta or, when treated as a subdivision of [[Tracheophyta]] (vascular plants), Polypodiopsida, although this name sometimes only refers to leptosporangiate ferns. Traditionally, all of the spore producing [[vascular plant]]s were informally denominated the [[pteridophyte]]s, rendering the term synonymous with ferns and [[fern allies]]. This can be confusing because members of the division Pteridophyta were also denominated pteridophytes (''sensu stricto'').

Traditionally, three discrete groups have been denominated ferns: two groups of eusporangiate ferns, the families [[Ophioglossaceae]] ([[Ophioglossum|adder's tongues]], [[moonwort]]s, and grape ferns) and [[Marattiaceae]]; and the leptosporangiate ferns. The Marattiaceae are a primitive group of tropical ferns with large, fleshy rhizomes and are now thought to be a [[sister group|sibling taxon]] to the leptosporangiate ferns. Several other groups of species were considered fern allies: the [[clubmoss]]es, [[spikemoss]]es, and [[Isoëtes|quillworts]] in [[Lycopodiophyta]]; the whisk ferns of [[Psilotaceae]]; and the horsetails of [[Equisetaceae]]. Since this grouping is [[Polyphyly|polyphyletic]], the term fern allies should be abandoned, except in a historical context.{{sfn|Christenhusz|Chase|2014}} More recent genetic studies demonstrated that the Lycopodiophyta are more distantly related to other [[vascular plant]]s, having radiated evolutionarily at the base of the vascular plant [[clade]], while both the whisk ferns and horsetails are as closely related to leptosporangiate ferns as the [[ophioglossoid fern]]s and [[Marattiaceae]]. In fact, the whisk ferns and ophioglossoid ferns are demonstrably a [[clade]], and the [[horsetail]]s and [[Marattiaceae]] are arguably another clade.

=== Molecular phylogenetics ===

Smith et al. (2006) carried out the first higher-level pteridophyte classification published in the [[molecular phylogenetic]] era, and considered the ferns as monilophytes, as follows:{{sfn|Smith et al.2006}}
* [[Division (botany)|Division]] [[Tracheophyta]] (tracheophytes) – vascular plants
** [[Subdivision (botany)|Sub division]] [[Euphyllophytina]] (euphyllophytes)
*** Infradivision [[Moniliformopses]] ('''monilophytes''')
*** Infradivision [[Spermatophyta]] – seed plants, ~260,000 species
** Subdivision [[Lycopodiophyta]] (lycophytes) – less than 1% of extant vascular plants

Molecular data, which remain poorly constrained for many parts of the plants' phylogeny, have been supplemented by morphological observations supporting the inclusion of Equisetaceae in the ferns, notably relating to the construction of their sperm and peculiarities of their roots.{{sfn|Smith et al.2006}}

The leptosporangiate ferns are sometimes called "true ferns".<ref>{{Cite book |last=Stace |first=Clive |author-link = Clive Stace |year=2010b |title=New Flora of the British Isles |edition=3rd |location=Cambridge, UK |publisher=Cambridge University Press |isbn=978-0-521-70772-5 |page=xxviii}}</ref> This 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. Rai and Graham (2010) broadly supported the primary groups, but queried their relationships, concluding that "at present perhaps the best that can be said about all relationships among the major lineages of monilophytes in current studies is that we do not understand them very well".<ref name=RaiGraham2010>{{Cite journal |last1=Rai |first1=Hardeep S. |last2=Graham |first2=Sean W. |year=2010 |title=Utility of a large, multigene plastid data set in inferring higher-order relationships in ferns and relatives (monilophytes) |journal=American Journal of Botany |volume=97 |issue=9 |pages=1444–1456 |doi=10.3732/ajb.0900305 |name-list-style=amp |pmid=21616899}}, p. 1450</ref> Grewe et al. (2013) confirmed the inclusion of horsetails within ferns ''sensu lato'', but also suggested that uncertainties remained in their precise placement.<ref name=Grew13/> Other classifications have raised Ophioglossales to the rank of a fifth class, separating the whisk ferns and ophioglossoid ferns.<ref name=Grew13/>

=== Phylogeny ===

The ferns are related to other groups as shown in the following cladogram:{{sfn|Christenhusz|Chase|2014}}{{sfn|Cantino et al|2007}}{{sfn|Chase|Reveal|2009}}{{sfn|Pteridophyte Phylogeny Group|2016}}
{{clade |style=line-height:140%;font-size:100%;
|label1= [[Tracheophyta]] |sublabel1= (vascular plants) 
|1={{clade
   |1= [[Lycopodiophyta|Lycophytes]] [[File:2021-03_Amsterdam_Island_-_lycopodium_clavatum_10.jpg|50px]]
   |label2= [[Euphyllophyta]] 
   |2={{clade
      |1='''Ferns''' [[File:California_Arena_Point_fern.jpg|70px]]
      |label2= [[Spermatophyta]] |sublabel2=(seed plants)
      |2={{clade
         |1=[[Gymnosperm]]s [[File:Flore_des_serres_v15_147a.jpg|50px]]
         |2=[[Angiosperm]]s [[File:160 Ranunculus repens.jpg|50px]]
         }}
      }}
   }}
}}

=== Nomenclature and subdivision ===

{{further|List of fern families}}

The classification of Smith et al. in 2006 treated ferns as four classes:{{sfn|Smith et al.2006}}{{sfn|Schuettpelz|2007|loc=Table I}}

* [[Equisetidae|Equisetopsida]] (Sphenopsida) – 1 order, [[Equisetales]] ([[Horsetail]]s) ~ 15 species
* [[Ophioglossidae|Psilotopsida]] – 2 orders ([[Psilotaceae|whisk ferns]] and [[ophioglossoid fern]]s) ~92 species 
* [[Marattiidae|Marattiopsida]] – 1 order, [[Marattiales]] ~ 150 species
* [[Polypodiidae (plant)|Polypodiopsida]] (Filicopsida) – 7 orders ([[leptosporangiate fern]]s) ~ 9,000 species

In addition they defined 11 orders and 37 families.{{sfn|Smith et al.2006}} That system was a consensus of a number of studies, and was further refined.<ref name=Grew13>{{cite journal |last=Grewe |first=Felix |title=Complete plastid genomes from Ophioglossum californicum, Psilotum nudum, and Equisetum hyemale reveal an ancestral land plant genome structure and resolve the position of Equisetales among monilophytes |journal=BMC Evolutionary Biology |year=2013 |volume=13 |issue=1 |pages=1–16 |doi=10.1186/1471-2148-13-8 |issn=1471-2148 |display-authors=etal |pmid=23311954 |pmc=3553075 |doi-access=free |bibcode=2013BMCEE..13....8G }}</ref><ref>{{cite journal |last=Karol |first=Kenneth G. |title=Complete plastome sequences of Equisetum arvense and Isoetes flaccida: implications for phylogeny and plastid genome evolution of early land plant lineages |journal=BMC Evolutionary Biology |year=2010|volume=10 |pages=321–336 |doi=10.1186/1471-2148-10-321 |issn=1471-2148 |pmid=20969798|pmc=3087542|issue=1|display-authors=etal |doi-access=free |bibcode=2010BMCEE..10..321K }}</ref> The phylogenetic relationships are shown in the following [[cladogram]] (to the level of orders).{{sfn|Smith et al.2006}}<ref>{{cite journal |last1=Li |first1=F-W |last2=Kuo |first2=L-Y |last3=Rothfels |first3=CJ |last4=Ebihara |first4=A |last5=Chiou |first5=W-L |display-authors=etal |year=2011 |title=rbcL and matK Earn Two Thumbs Up as the Core DNA Barcode for Ferns |journal=PLOS ONE |volume=6 |issue=10|page=e26597 |doi=10.1371/journal.pone.0026597 |pmid=22028918 |pmc=3197659|bibcode=2011PLoSO...626597L |doi-access=free }}</ref><ref name=Grew13/> This division into four major clades was then confirmed using [[plant morphology|morphology]] alone.{{sfn|Schneider et al|2009}}

{{Fern cladogram.show(Orders & Outgroups)}}

Subsequently, [[Mark W. Chase|Chase]] and [[James L. Reveal|Reveal]] considered both lycopods and ferns as subclasses of a class Equisetopsida ([[Embryophyta]]) encompassing all land plants. This is referred to as [[Equisetopsida sensu lato|Equisetopsida]] ''[[sensu lato]]'' to distinguish it from the narrower use to refer to horsetails alone, [[Equisetopsida]] ''sensu stricto''. They placed the lycopods into subclass Lycopodiidae and the ferns, keeping the term monilophytes, into five subclasses, Equisetidae, Ophioglossidae, Psilotidae, Marattiidae and Polypodiidae, by dividing Smith's Psilotopsida into its two orders and elevating them to subclass (Ophioglossidae and Psilotidae).{{sfn|Chase|Reveal|2009}} Christenhusz et al.{{efn|President, International Association of Pteridologists}} (2011) followed this use of subclasses but recombined Smith's Psilotopsida as Ophioglossidae, giving four subclasses of ferns again.{{sfn|Christenhusz et al|2011}}

[[Christenhusz]] and [[Mark Chase|Chase]] (2014) developed a new classification of ferns and lycopods. They used the term Polypodiophyta for the ferns, subdivided like Smith et al. into four groups (shown with equivalents in the Smith system), with 21 families, approximately 212 genera and 10,535 species;{{sfn|Christenhusz|Chase|2014}}
* [[Equisetidae]] (=Equisetopsida) – [[monotypic]] (Equisetales, [[Equisetaceae]], ''[[Equisetum]]'') horsetails ~ 20 species)
* [[Ophioglossidae]] (=Psilotopsida) – 2 monotypic orders ~ 92 species
* [[Marattiidae]] (=Marattiopsida) – 1 monotypic order (Marattiales, [[Marattiaceae]], 2 subfamilies) ~ 130 species
* [[Polypodiidae (plant)|Polypodiidae]] (=Polypodiopsida) – 7 orders

This was a considerable reduction in the number of families from the 37 in the system of Smith et al., since the approach was more that of [[lumping]] rather than splitting. For instance a number of families were reduced to subfamilies. Subsequently, a [[Scientific consensus|consensus]] group was formed, the [[Pteridophyte Phylogeny Group]] (PPG), analogous to the [[Angiosperm Phylogeny Group]], publishing their first complete classification in November 2016. They recognise ferns as a class, the Polypodiopsida, with four subclasses as described by Christenhusz and Chase, and which are phylogenetically related as in this cladogram:

{|class="wikitable"
|-
! colspan=1 |Christenhusz and Chase 2014{{sfn|Pteridophyte Phylogeny Group|2016}}
! colspan=1 |Nitta et al. 2022<ref name="Polypodiopsida"/> and Fern Tree of life<ref>{{cite web |year=2024 |title=Tree viewer: interactive visualization of FTOL |url=https://fernphy.github.io/viewer.html |version=FTOL v1.7.0 |access-date=1 May 2025}}</ref>
|- 
|style="vertical-align:top|
{{Clade |style=font-size:90%;line-height:80%
|label1='''Polypodiopsida'''
|1={{clade
  |label1=[[Equisetidae]]
  |1=[[Equisetales]]
  |2={{clade
    |label1=[[Ophioglossidae]]
    |1={{clade
       |1=[[Ophioglossales]]
       |2=[[Psilotales]]
       }}
    |2={{clade
      |label1=[[Marattiidae]]
      |1=[[Marattiales]]
      |label2=[[Polypodiidae (plant)|Polypodiidae]]
      |2={{clade
        |1=[[Osmundales]]
        |2={{clade
          |1=[[Hymenophyllales]]
          |2={{clade
            |1=[[Gleicheniales]]
            |2={{clade
              |1=[[Schizaeales]]
              |2={{clade
                |1=[[Salviniales]]
                |2={{clade
                  |1=[[Cyatheales]]
                  |2=[[Polypodiales]]
                   }}
                 }}
               }}
             }}
           }}
         }}
       }}
     }}
   }}
}}
|
{{Clade |style=font-size:90%;line-height:80%
|1={{clade
  |1={{clade
    |label1=[[Equisetidae]]
    |1=[[Equisetales]]
    |label2=[[Ophioglossidae]]
    |2={{clade
      |1=[[Psilotales]]
      |2=[[Ophioglossales]]
       }}
     }}
  |2={{clade
    |label1=[[Marattiidae]]
    |1=[[Marattiales]]
    |label2=[[Polypodiidae (plant)|Polypodiidae]]
    |2={{clade
      |1=[[Osmundales]]
      |2={{clade
        |1=[[Hymenophyllales]]
        |2={{clade
          |1=[[Gleicheniales]]
          |2={{clade
            |1=[[Dipteridales]]
            |2={{clade
              |1=[[Schizaeales]]
              |2={{clade
                |1={{clade
                  |1=[[Salviniales]]
                  |2=[[Cyatheales]]
                   }}
                |2=[[Polypodiales]]
                 }}
               }}
             }}
           }}
         }}
       }}
     }}
   }}
}}
|}

In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), the Polypodiopsida consist of four subclasses, 11 orders, 48 families, 319 genera, and an estimated 10,578 species.{{sfn|Christenhusz|Byng|2016}} Thus Polypodiopsida in the broad sense (''sensu lato'') as used by the PPG (Polypodiopsida ''sensu'' PPG I) needs to be distinguished from the narrower usage (''sensu stricto'') of Smith et al. (Polypodiopsida ''sensu'' Smith et al.){{sfn|Pteridophyte Phylogeny Group|2016}} Classification of ferns remains unresolved and controversial with competing viewpoints ([[splitting vs lumping]]) between the systems of the PPG on the one hand and Christenhusz and Chase on the other, respectively. In 2018, Christenhusz and Chase explicitly argued against recognizing as many genera as PPG I.{{sfn|Schuettpelz et al|2018}}{{sfn|Christenhusz |Chase|2018}}

{|class="wikitable" style= "font-size: 87%"
|+ Comparison of fern subdivisions in some classifications
|-
! Smith et al. (2006){{sfn|Smith et al.2006}} !! Chase & Reveal (2009){{sfn|Chase|Reveal|2009}} !! Christenhusz et al. (2011){{sfn|Christenhusz et al|2011}} !! Christenhusz & Chase (2014, 2018){{sfn|Christenhusz|Chase|2014}}{{sfn|Christenhusz et al|2018}} !! PPG I (2016){{sfn|Pteridophyte Phylogeny Group|2016}}
|-
|'''ferns'''<br/>(no rank) ||'''monilophytes'''<br/>(no rank) ||'''ferns (monilophytes)'''<br/>(no rank) ||'''ferns (Polypodiophyta)'''<br/>(no rank) ||&nbsp;'''Class Polypodiopsida'''
|-
|Class Equisetopsida ||&nbsp;&nbsp;Subclass Equisetidae ||&nbsp;&nbsp;Subclass Equisetidae ||&nbsp;&nbsp;Subclass Equisetidae ||&nbsp;Subclass [[Equisetidae]]
|-
|Class Psilotopsida ||&nbsp;&nbsp;Subclass Ophioglossidae<br/>&nbsp;&nbsp;Subclass Psilotidae ||&nbsp;&nbsp;Subclass Ophioglossidae ||&nbsp;&nbsp;Subclass Ophioglossidae ||&nbsp;Subclass [[Ophioglossidae]]
|-
|Class Marattiopsida ||&nbsp;&nbsp;Subclass Marattiidae ||&nbsp;&nbsp;Subclass Marattiidae ||&nbsp;&nbsp;Subclass Marattiidae ||&nbsp;Subclass [[Marattiidae]]
|-
|Class Polypodiopsida ||&nbsp;&nbsp;Subclass Polypodiidae ||&nbsp;&nbsp;Subclass Polypodiidae ||&nbsp;&nbsp;Subclass Polypodiidae ||&nbsp;Subclass [[Polypodiidae (plant)|Polypodiidae]]
|}

=== Evolution and biogeography ===

Fern-like taxa (''[[Wattieza]]'') first appear in the fossil record in the middle [[Devonian]] period, ca. 390&nbsp;[[Mya (unit)|Mya]]. 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.{{sfn|UCMP|2019}}{{sfn|Stein et al|2007}}{{sfn|Berry|2009}}{{sfn|Bomfleur et al|2014}} Ferns evolved to cope with low-light conditions present under the canopy of angiosperms.

Remarkably, the [[Photoreceptor protein|photoreceptor]] neochrome in the two orders Cyatheales and Polypodiales, integral to their adaptation to low-light conditions, was obtained via [[horizontal gene transfer]] from [[hornwort]]s, a [[bryophyte]] lineage.<ref>{{cite journal |last1=Li |first1=F.-W. |last2=Villarreal |first2=J. C. |last3=Kelly |first3=S. |last4=Rothfels |first4=C. J. |last5=Melkonian |first5=M. |last6=Frangedakis |first6=E. |last7=Ruhsam |first7=M. |last8=Sigel |first8=E. M. |last9=Der |first9=J. P. |last10=Pittermann |first10=J. |last11=Burge |first11=D. O. |last12=Pokorny |first12=L. |last13=Larsson |first13=A. |last14=Chen |first14=T. |last15=Weststrand |first15=S. |last16=Thomas |first16=P. |last17=Carpenter |first17=E. |last18=Zhang |first18=Y. |last19=Tian |first19=Z. |last20=Chen |first20=L. |last21=Yan |first21=Z. |last22=Zhu |first22=Y. |last23=Sun |first23=X. |last24=Wang |first24=J. |last25=Stevenson |first25=D. W. |last26=Crandall-Stotler |first26=B. J. |last27=Shaw |first27=A. J.|author28-link=Michael Deyholos |last28=Deyholos |first28=M. K. |last29=Soltis |first29=D. E. |last30=Graham |first30=S. W. |last31=Windham |first31=M. D. |last32=Langdale |first32=J. A. |last33=Wong |first33=G. K.-S. |last34=Mathews |first34=S. |last35=Pryer |first35=K. M. |display-authors=3 |title=Horizontal transfer of an adaptive chimeric photoreceptor from bryophytes to ferns |journal=Proceedings of the National Academy of Sciences |date=6 May 2014 |volume=111 |issue=18 |pages=6672–6677 |doi=10.1073/pnas.1319929111|pmid=24733898 |pmc=4020063 |bibcode=2014PNAS..111.6672L |doi-access=free }}</ref>

Due to the very large genome seen in most ferns, it was suspected they might have gone through [[Paleopolyploidy|whole genome duplications]], but [[DNA sequencing]] has shown that their genome size is caused by the accumulation of mobile DNA like [[Transposable element|transposons]] and other genetic elements that infect genomes and get copied over and over again.<ref>[https://www.science.org/content/article/genes-seeds-arose-early-plant-evolution-ferns-reveal Genes for seeds arose early in plant evolution, ferns reveal]</ref>

Ferns appear to have evolved [[extrafloral nectaries]] 135 million years ago, nearly simultaneously with the trait's evolution in angiosperms. However, nectary-associated diversifications in ferns did not hit their stride until nearly 100 million years later, in the [[Cenozoic]]. There is weak support for the rise of fern-feeding arthropods driving this diversification.<ref>{{Cite journal |last1=Suissa |first1=Jacob S. |last2=Li |first2=Fay-Wei |last3=Moreau |first3=Corrie S. |date=2024-05-24 |title=Convergent evolution of fern nectaries facilitated independent recruitment of ant-bodyguards from flowering plants |journal=Nature Communications |language=en |volume=15 |issue=1 |pages=4392 |doi=10.1038/s41467-024-48646-x |issn=2041-1723|doi-access=free |pmid=38789437 |pmc=11126701 |bibcode=2024NatCo..15.4392S }}</ref>

== Distribution and habitat ==

Ferns are widespread in their distribution, with the greatest richness in the tropics and least in arctic areas. The greatest diversity occurs in tropical rainforests.{{sfn|EB|2019}} New Zealand, for which the fern is a symbol, has about 230 species, distributed throughout the country.{{sfn|SLH|2018}} It is a common plant in [[Europe]]an forests.

== Ecology ==

Fern species live in a wide variety of [[habitat]]s, from remote [[mountain]] elevations, to dry [[desert]] rock faces, bodies of water or open fields. Ferns in general may be thought of as largely being specialists in marginal habitats, often succeeding in places where various environmental factors limit the success of [[flowering plant]]s. Some ferns are among the world's most serious weed species, including the [[bracken]] fern growing in the Scottish highlands, or the mosquito fern (''[[Azolla]]'') growing in tropical lakes, both species forming large aggressively spreading colonies. There are four particular types of habitats that ferns are found in: moist, shady [[forest]]s; crevices in rock faces, especially when sheltered from the full sun; acid wetlands including [[bog]]s and [[swamp]]s; and tropical [[tree]]s, where many species are [[epiphyte]]s (something like a quarter to a third of all fern species).{{sfn|Schuettpelz|2007|loc=Part I}}

Especially the epiphytic ferns have turned out to be hosts of a huge diversity of invertebrates. It is assumed that [[bird's-nest fern]]s alone contain up to half the invertebrate biomass within a hectare of [[rainforest]] canopy.<ref>{{Cite web|url=https://www.science.org/content/article/ferns-brimming-life|title=Ferns Brimming With Life|date=2 June 2004|website=Science &#124; AAAS}}</ref>

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

The spores are rich in [[lipid]]s, [[protein]] and [[calories]], so some vertebrates eat these. The [[European woodmouse]] (''Apodemus sylvaticus'') has been found to eat the spores of ''[[Culcita macrocarpa]]'', and the [[bullfinch]] (''Pyrrhula murina'') and the [[New Zealand lesser short-tailed bat]] (''Mystacina tuberculata'') also eat fern spores.<ref>{{cite news|url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8523000/8523825.stm|title=A mouse that eats ferns like a dinosaur|last=Walker|first=Matt|date=19 February 2010|publisher=BBC Earth News|access-date=2010-02-20}}</ref>

<gallery class=center mode=nolines widths=300 heights=250>
File:CowellFerns.JPG|In undergrowth below [[Sequoia sempervirens|coast redwoods]], California
File:FernBedInForest.jpg|Fern bed under a forest canopy, Virginia
File:Samambaia fern.jpg|On a wall
File:Harts Tongue Fern on the Great Orme - geograph.org.uk - 345785.jpg|''[[Asplenium]]'' hart's tongue fern in a [[wikt:gryke|gryke]] in [[limestone pavement]]
File:... epiphytic fern (49095803342).jpg|[[Epiphyte|Epiphytic]] ferns in India
File:Canning_rv_azolla_10_gnangarra.jpg|''[[Azolla]]'' duckweed fern covering<br/>the [[Canning River]], Western Australia
</gallery>

=== Life cycle ===

Ferns are [[vascular plant]]s differing from [[lycophyte]]s by having true [[leaf|leaves]] (megaphylls), which are often [[pinnate]]. They differ from [[spermatophyte|seed plant]]s ([[gymnosperm]]s and [[angiosperm]]s) in reproducing by means of spores and lacking [[flower]]s and [[seed]]s. Like all [[embryophyte|land plants]], they have a [[biological life cycle|life cycle]] referred to as [[alternation of generations]], characterized by alternating [[diploid]] [[sporophyte|sporophytic]] and [[haploid]] [[gametophyte|gametophytic]] phases. The diploid sporophyte has 2''n'' paired [[chromosome]]s, where ''n'' varies from species to species. The haploid gametophyte has ''n'' unpaired chromosomes, i.e. half the number of the sporophyte. The gametophyte of ferns is a free-living organism, whereas the gametophyte of the gymnosperms and angiosperms is dependent on the sporophyte.

The life cycle of a typical fern proceeds as follows:
# A diploid sporophyte phase produces haploid [[spore]]s by [[meiosis]] (a process of cell division which reduces the number of chromosomes by a half).
# A spore grows into a free-living haploid gametophyte by [[mitosis]] (a process of cell division which maintains the number of chromosomes). The gametophyte 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 diploid sporophyte (the typical fern plant).

Sometimes a gametophyte can give rise to sporophyte traits like roots or sporangia without the rest of the sporophyte.<ref>[https://books.google.com/books?id=x494WF2PvbsC&pg=PA324 The Ferns (Filicales): Volume 1, Analytical Examination of the Criteria of Comparison: Treated Comparatively with a View to their Natural Classification]</ref>

<gallery class=center mode=nolines widths=300 heights=250>
File:Monarch fern sori.jpeg|[[Sorus]] of [[monarch fern]], with [[sporangium]]
File:Onoclea sensibilis 3 crop.JPG|Gametophyte ([[thallus]]) and sporophyte (ascendant frond) of ''[[Onoclea sensibilis]]''
</gallery>

== Uses ==

Ferns are not as important economically as seed plants, but have considerable importance in some societies. Some ferns are used for food, including the fiddleheads of ''Pteridium aquilinum'' ([[bracken]]), ''Matteuccia struthiopteris'' ([[ostrich fern]]), and ''Osmundastrum cinnamomeum'' ([[cinnamon fern]]). ''[[Diplazium esculentum]]'' is also used in the tropics (for example in ''budu pakis'', a traditional dish of [[Brunei]]<ref>{{cite book|title=Indigenous Fermented Foods of Southeast Asia|year=2015}}</ref>) as food. Tubers from the "para", ''[[Ptisana salicina]]'' (king fern) are a traditional food in [[New Zealand]] and the [[Oceania|South Pacific]]. Fern tubers were used for food 30,000 years ago in Europe.<ref>Van Gilder Cooke, Sonia (23 October 2010). [https://www.newscientist.com/article/dn19597-stone-age-humans-liked-their-burgers-in-a-bun.html "Stone Age humans liked their burgers in a bun".] ''[[New Scientist]]'', p. 18.</ref><ref>Revedin, Anna et al. (18 October 2010). [http://www.pnas.org/cgi/doi/10.1073/pnas.1006993107 "Thirty thousand-year-old evidence of plant food processing".] ''[[PNAS]]''.</ref> Fern tubers were used by the [[Guanches]] to make [[gofio]] in the [[Canary Islands]]. Ferns are generally not known to be poisonous to humans.<ref name="edible plant">{{cite book | title=The Official Pocket Edible Plant Survival Manual | publisher=Freedom and Liberty Foundation Press | last=Pelton |first=Robert | year=2011 | page=25 | id=[[Barnes & Noble|BNID]] [http://www.barnesandnoble.com/w/?ean=2940013382145 2940013382145]}}</ref> [[Licorice fern]] [[rhizome]]s were chewed by the natives of the [[Pacific Northwest]] for their flavor.<ref>{{Cite book |last=Moerman |first=Daniel E. |url=https://books.google.com/books?id=iYhjlKR7GZEC |title=Native American Food Plants: An Ethnobotanical Dictionary |date=2010-10-27 |publisher=Timber Press |isbn=978-1-60469-189-4 |pages=190 |language=en}}</ref> Some species of ferns are [[carcinogenic]], and the British Royal Horticultural Society has advised not to consume any species for health reasons of both humans and livestock.<ref>{{cite web|title=Dol Sot Bibimbap|url=http://apps.rhs.org.uk/advicesearch/Profile.aspx?pid=445|access-date=2011-12-19|archive-url=https://web.archive.org/web/20111111190952/http://apps.rhs.org.uk/advicesearch/profile.aspx?PID=445|archive-date=2011-11-11|url-status=dead}}</ref>

Ferns of the genus ''Azolla'', commonly known as water fern or mosquito ferns are very small, floating plants that do not resemble ferns. The mosquito ferns 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.

Ferns have proved resistant to phytophagous insects. The gene that express the protein Tma12 in an edible fern, ''[[Tectaria macrodonta]]'', has been transferred to cotton plants, which became resistant to [[whitefly]] infestations.<ref>{{Cite journal|title=Expression of an insecticidal fern protein in cotton protects against whitefly|first1=Anoop Kumar|last1=Shukla|first2=Santosh Kumar|last2=Upadhyay|first3=Manisha|last3=Mishra |first4=Sharad|last4=Saurabh|first5=Rahul |last5=Singh|first6=Harpal|last6=Singh|first7=Nidhi|last7=Thakur|first8=Preeti|last8=Rai|first9=Paras|last9=Pandey|first10=Aradhana L.|last10=Hans|first11=Subhi|last11=Srivastava |first12=Vikram|last12=Rajapure |first13=Sunil Kumar|last13=Yadav |first14=Mithlesh Kumar |last14=Singh |first15=Jitendra |last15=Kumar|first16=K.|last16=Chandrashekar |first17=Praveen C. |last17=Verma |first18=Ajit Pratap|last18=Singh|first19=K. N.|last19=Nair|first20=Smrati|last20=Bhadauria |first21=Muhammad |last21=Wahajuddin |first22=Sarika|last22=Singh|first23=Sharad |last23=Sharma|first24=null|last24=Omkar |first25=Ram Sanmukh |last25=Upadhyay|first26=Shirish A. |last26=Ranade|first27=Rakesh|last27=Tuli|first28=Pradhyumna Kumar|last28=Singh |display-authors=3 |date=26 October 2016 |journal=Nature Biotechnology |volume=34 |issue=10 |pages=1046–1051 |doi=10.1038/nbt.3665 |pmid=27598229 |s2cid=384923}}</ref>

Many ferns are grown in [[horticulture]] as landscape plants, for [[foliage|cut foliage]] and as [[houseplant]]s, especially the Boston fern (''[[Nephrolepis exaltata]]'') and other members of the genus ''[[Nephrolepis]]''. The [[Asplenium nidus|bird's nest fern]] (''Asplenium nidus'') is also popular, as are the [[staghorn fern]]s (genus ''Platycerium''). Perennial (also known as hardy) ferns planted in gardens in the northern hemisphere also have a considerable following.<ref>{{Cite web |title=Ferns: A Classic Shade Garden Plant |url=https://extension.sdstate.edu/ferns-classic-shade-garden-plant |access-date=2023-05-30 |website=extension.sdstate.edu}}</ref>

Several ferns, such as bracken<ref name=CABIPteridium>{{cite web|date=2018 |title=Datasheet: ''Pteridium aquilinum'' (bracken) |url=https://www.cabi.org/isc/datasheet/45596 |publisher=CAB International |access-date=11 February 2019 }}</ref> and ''Azolla''<ref name=CABIAzolla>{{cite web|date=2018 |title=Datasheet: ''Azolla filiculoides'' (water fern) |url=https://www.cabi.org/isc/datasheet/8119 |publisher=CAB International |access-date=11 February 2019 }}</ref> species are noxious [[weed]]s or [[invasive species]]. Further examples include Japanese climbing fern (''[[Lygodium japonicum]]''), [[sensitive fern]] (''Onoclea sensibilis'') and Giant water fern (''[[Salvinia molesta]]''), one of the world's worst aquatic weeds.<ref>{{Cite web |title={{!}} Center for Aquatic and Invasive Plants {{!}} University of Florida, IFAS |url=https://plants.ifas.ufl.edu/plant-directory/salvinia-molesta/ |access-date=2023-05-30 |website=plants.ifas.ufl.edu}}</ref><ref>{{Cite book|last=Moran|first=Robbin|title=A Natural History of Ferns|year=2004|publisher=Timber Press |isbn=0-88192-667-1}}</ref> The important fossil fuel [[coal]] consists of the remains of primitive plants, including ferns.<ref>{{Cite web |title=Fossils, Kentucky Geological Survey, University of Kentucky |url=https://www.uky.edu/KGS/fossils/fossil-pennsylvanianPlants.php |access-date=2023-05-30 |website=www.uky.edu}}</ref>

== Culture ==

[[File:Nature print, Alois Auer.jpg|thumb|upright=1.2|Ferns in the [[Victorian era]]: ''Blätter des Manns Walfarn'' by [[Alois Auer]], Vienna: Imperial Printing Office, 1853]]

=== Pteridology ===

The study of ferns and other pteridophytes is called '''pteridology'''. A '''pteridologist''' is a specialist in the study of pteridophytes in a broader sense that includes the more distantly related [[lycophyte]]s.

=== Pteridomania ===

[[Pteridomania]] was a [[Victorian era]] [[Fads and trends|craze]] which involved fern [[collecting]] and fern motifs in [[decorative art]] including [[pottery]], [[glass]], [[metal]]s, [[textile]]s, [[wood]], [[printing|printed paper]], and [[sculpture]] "appearing on everything from [[infant baptism|christening]] presents to [[gravestone]]s 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.<ref>{{cite journal |last=Boyd |first=Peter D. A. |date=2 January 2002 |title=Pteridomania – the Victorian passion for ferns |url=http://www.peterboyd.com/pteridomania.htm |journal=Antique Collecting |version=Revised: web version |volume=28 |issue=6 |pages=9–12 |access-date=2 October 2007}}</ref>

=== Other applications ===

[[File:Barnsley fern plotted with VisSim.PNG|thumb|right|[[Barnsley fern]] created using a [[chaos game]], through an [[Iterated function system]]<ref name=Fractals/>]]

The '''Barnsley fern''' is a [[fractal]] named after the British [[mathematician]] [[Michael Barnsley]] who first described it in his book ''Fractals Everywhere''. A [[Self-similarity|self-similar]] structure is described by a mathematical function, applied repeatedly at different scales to create a frond pattern.<ref name=Fractals>[https://books.google.com/books?id=oh7NoePgmOIC Fractals Everywhere], Boston, MA: Academic Press, 1993, {{ISBN|0-12-079062-9}}</ref>

The dried form of ferns was used in other arts, such 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''.

[[Fern bar]]s were popular in America in the 1970s and 80s.

=== Folklore ===

Ferns figure in folklore, for example in legends about mythical flowers or seeds.{{sfn|May|1978}} In [[Slavic folklore]], ferns are believed to bloom once a year, during the [[Ivan Kupala Day|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, [[Finland|Finnish]] tradition holds that one who finds the [[seed]] of a fern in bloom on [[Midsummer]] night will, by possession of it, be guided and be able to travel invisibly to the locations where eternally blazing [[Will o' the wisp]]s called ''[[aarnivalkea]]'' mark the spot of hidden [[treasure]]. These spots are protected by a spell that prevents anyone but the fern-seed holder from ever knowing their locations.<ref>{{cite web |url=http://www.saunalahti.fi/~marian1/gourmet/season5a.htm |title=Traditional Finnish Midsummer celebration |publisher=Saunalahti.fi |access-date=2013-09-07 |archive-date=19 September 2011 |archive-url=https://web.archive.org/web/20110919201014/http://www.saunalahti.fi/~marian1/gourmet/season5a.htm |url-status=dead }}</ref> In Wicca, ferns are thought to have magical properties such as a dried fern can be thrown into hot coals of a fire to exorcise evil spirits, or smoke from a burning fern is thought to drive away snakes and such creatures.<ref name="Cunningham">{{cite book |last=Cunningham |first=Scott |author-link=Scott Cunningham |title=Cunningham's Encyclopedia of Magical Herbs |date=1999 |publisher=Llewellyn |page=102}}</ref>

=== New Zealand ===

Ferns are the national emblem of New Zealand and feature on its passport and in the design of its national airline, [[Air New Zealand]], and of its rugby team, the [[All Blacks]].

==Organisms confused with ferns==

=== Misnomers ===

Several non-fern plants (and even animals) are called ferns and are sometimes confused with ferns. These include:

* Asparagus fern—This may apply to one of several species of the [[monocotyledon|monocot]] genus ''[[Asparagus (genus)|Asparagus]]'', which are flowering plants.
* Sweetfern—A flowering shrub of the genus ''[[Comptonia (plant)|Comptonia]]''.
* [[Air fern]]—A group of [[animal]]s called [[hydrozoa]]ns that are distantly related to [[jellyfish]] and [[coral]]s. 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 [[Colony (biology)|colonial animal]].
* Fern bush—''[[Chamaebatiaria|Chamaebatiaria millefolium]]''—a rose family shrub with fern-like leaves.
* Fern tree—''[[Jacaranda mimosifolia]]''—an [[ornamental tree]] of the order [[Lamiales]].
* Fern leaf tree—''[[Filicium decipiens]]''—an [[ornamental tree]] of the order [[Sapindales]].

=== Fern-like flowering plants ===

Some [[flowering plant]]s such as [[Arecaceae|palms]] and members of the [[Apiaceae|carrot family]] have [[pinnate]] leaves that somewhat resemble fern fronds. However, these plants have fully developed seeds contained in fruits, rather than the microscopic spores of ferns.

== See also ==

{{div col|colwidth=30em}}
* [[British Pteridological Society]]
* [[Chirosia betuleti]] – Fern gall
* [[Fern spike]]
* [[Fern sports]]
* [[Paisley (design)]]
* [[Pteridophyte]]
* [[Silver fern flag]]
{{div col end}}

== Notes ==
{{Notelist}}

== References ==
{{Reflist|30em}}

== Bibliography ==
{{Refbegin|30em}}

=== Books ===

* {{cite book |last1=Christenhusz |first1=Maarten M. J. |last2=Fay |first2=Michael |last3=Byng |first3=James W. |author-link1=Maarten Christenhusz |author-link2=Michael Francis Fay |author-link3=James W. Byng |title=The Global Flora: Special Edition: GLOVAP Nomenclature Part 1 |url=https://books.google.com/books?id=DX60DwAAQBAJ |date=2018 |publisher=Plant Gateway Limited |isbn=978-0-9929993-6-0 |ref={{harvid|Christenhusz et al|2018}}}}
* {{cite book |last=Linnaeus |first=Carl |author-link=Carl Linnaeus |title=Species Plantarum: exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas |url=https://www.biodiversitylibrary.org/bibliography/669#/summary |year=1753 |volume=1 |chapter=Cryptogamia: Filices Musci |chapter-url=https://www.biodiversitylibrary.org/item/13830#page/503/mode/1up |pages=1061–1100, 1100–1130 |publisher=Impensis Laurentii Salvii |location=Stockholm, Sweden}}, ''see also'' [[Species Plantarum]]
* Lord, Thomas R. (2006). ''Ferns and Fern Allies of Pennsylvania''. Indiana, Pennsylvania: Pinelands Press. [http://www.paferns.com/ Ferns and Fern Allies of Pennsylvania – Thomas Reeves Lord].
* Moran, Robbin C. (2004). ''A Natural History of Ferns''. Portland, Oregon: Timber Press. {{ISBN|0-88192-667-1}}
* {{cite book |last1=Ranker |first1=Tom A. |last2=Haufler |first2=Christopher H. |title=Biology and Evolution of Ferns and Lycophytes |url=https://books.google.com/books?id=js9JnwEACAAJ |date=2008 |publisher=[[Cambridge University Press]] |isbn=978-0-521-87411-3}}
* {{cite book |last=Swartz |first=Olof |author-link=Olof Swartz |title=Synopsis filicum: earum genera et species systematice complectens: adjectis lycopodineis, et descriptionibus novarum et rariorum specierum: cum tabulis aeneis quinque |date=1806 |publisher=Impensis Bibliopolii novi academici |location=[[Kiliae]] |url=https://www.biodiversitylibrary.org/bibliography/81948#/summary}}

=== Journal articles ===

* {{cite journal |last=Berry |first=Chris |title=The Middle Devonian plant collections of Francois Stockmans reconsidered. |journal=[[Geologica Belgica]] |date=2009 |volume=12 |issue=1–2 |pages=25–30 |url=https://popups.uliege.be/1374-8505/index.php?id=2633&file=1}}
* {{cite journal |last1=Bomfleur |first1=B. |last2=McLoughlin |first2=S. |last3=Vajda |first3=V. |title=Fossilized Nuclei and Chromosomes Reveal 180 Million Years of Genomic Stasis in Royal Ferns |url=http://nrm.diva-portal.org/smash/get/diva2:719316/FULLTEXT01 |journal=[[Science (journal)|Science]] |date=20 March 2014 |volume=343 |issue=6177 |pages=1376–1377 |doi=10.1126/science.1249884 |pmid=24653037 |bibcode=2014Sci...343.1376B |s2cid=38248823 |ref={{harvid|Bomfleur et al|2014}}}}
* {{cite journal |last1=Cantino |first1=Philip D. |last2=Doyle |first2=James A. |last3=Graham |first3=Sean W. |last4=Judd |first4=Walter S. |author-link4=Walter S. Judd |last5=Olmstead |first5=Richard G. |last6=Soltis |first6=Douglas E. |author-link6=Douglas Soltis |last7=Soltis |first7=Pamela S. |author-link7=Pamela Soltis |last8=Donoghue |first8=Michael J. |author-link8=Michael Donoghue |title=Towards a Phylogenetic Nomenclature of Tracheophyta |journal=[[Taxon (journal)|Taxon]] |date=1 August 2007 |volume=56 |issue=3 |pages=822 |doi=10.2307/25065865 |ref={{harvid|Cantino et al|2007}} |jstor=25065865}}
* {{cite journal |last1=Chase |first1=Mark W. |author-link1=Mark W. Chase |last2=Reveal |first2=James L. |author-link2=James L. Reveal |name-list-style=amp |year=2009 |title=A phylogenetic classification of the land plants to accompany APG III |journal=[[Botanical Journal of the Linnean Society]] |volume=161 |issue=2 |pages=122–127 |doi=10.1111/j.1095-8339.2009.01002.x |doi-access=free}}
* {{cite journal |last1=Christenhusz |first1=Maarten J. M. |last2=Byng |first2=J. W. |author-link1=Maarten Christenhusz |author-link2=James W. Byng |name-list-style=amp |year=2016 |title=The number of known plants species in the world and its annual increase |journal=[[Phytotaxa]] |volume=261 |pages=201–217 |url=http://biotaxa.org/Phytotaxa/article/download/phytotaxa.261.3.1/20598 |doi=10.11646/phytotaxa.261.3.1 |issue=3 |publisher=Magnolia Press |doi-access=free}}
* {{cite journal |last1=Christenhusz |first1=Maarten J. M. |author-link1=Maarten J. M. Christenhusz |last2=Zhang |first2=X. C. |last3=Schneider |first3=H. |title=A linear sequence of extant families and genera of lycophytes and ferns |journal=[[Phytotaxa]] |date=18 February 2011 |volume=19 |issue=1 |pages=7 |doi=10.11646/phytotaxa.19.1.2 |ref={{harvid|Christenhusz et al|2011}} |doi-access=free|hdl=10138/28042 |hdl-access=free }}
* {{cite journal |last1=Christenhusz |first1=Maarten J. M. |author-link1=Christenhusz |last2=Chase |first2=Mark W. |author-link2=Mark W. Chase |year=2014 |title=Trends and concepts in fern classification |journal=[[Annals of Botany]] |volume=113 |issue=4 |pages=571–594 |doi=10.1093/aob/mct299 |pmid=24532607 |pmc=3936591}}
* {{cite journal |last1=Christenhusz |first1=Maarten J. M. |last2=Chase |first2=Mark W. |author-link1=Maarten Christenhusz |author-link2=Mark W. Chase |title=PPG recognises too many fern genera |journal=[[Taxon (journal)|Taxon]] |date=1 June 2018 |volume=67 |issue=3 |pages=481–487 |doi=10.12705/673.2 |doi-access=free}}
* {{Cite journal |last1=May |first1=Lenore Wile |title=The economic uses and associated folklore of ferns and fern allies |journal=[[The Botanical Review]] |year=1978 |volume=44 |issue=4 |pages=491–528 |doi=10.1007/BF02860848 |bibcode=1978BotRv..44..491M |s2cid=42101599}}
* {{cite journal |last1=Melan |first1=M. A. |last2=Whittier |first2=D. P. |year=1990 |title=Effects of Inorganic Nitrogen Sources on Spore Germination and Gametophyte Growth in Botrychium Dissectum |journal=Plant, Cell and Environment |volume=13 |issue=5 |pages=477–482 |doi=10.1111/j.1365-3040.1990.tb01325.x |bibcode=1990PCEnv..13..477M}}
* {{cite journal |last1=Pryer |first1=Kathleen M. |last2=Schneider |first2=Harald |last3=Smith |first3=Alan R. |last4=Cranfill |first4=Raymond |last5=Wolf |first5=Paul G. |last6=Hunt |first6=Jeffrey S. |last7=Sipes |first7=Sedonia D. |year=2001 |title=Horsetails and ferns are a monophyletic group and the closest living relatives to seed plants |journal=Nature |volume=409 |issue=6820 |pages=618–622 |doi=10.1038/35054555 |pmid=11214320 |bibcode=2001Natur.409..618S |s2cid=4367248}}
* {{cite journal |last1=Pryer |first1=Kathleen M. |last2=Schuettpelz |first2=Eric |last3=Wolf |first3=Paul G. |last4=Schneider |first4=Harald |last5=Smith |first5=Alan R. |last6=Cranfill |first6=Raymond |year=2004 |title=Phylogeny and evolution of ferns (monilophytes) with a focus on the early leptosporangiate divergences |journal=American Journal of Botany |volume=91 |issue=10 |pages=1582–1598 |doi=10.3732/ajb.91.10.1582 |pmid=21652310}}
* {{cite journal |last1=Pteridophyte Phylogeny Group |title=A community-derived classification for extant lycophytes and ferns |journal=Journal of Systematics and Evolution |date=November 2016 |volume=54 |issue=6 |pages=563–603 |doi=10.1111/jse.12229 |s2cid=39980610 |doi-access=free}}
* {{cite journal |last1=Schneider |first1=Harald |last2=Smith |first2=Alan R. |last3=Pryer |first3=Kathleen M. |title=Is Morphology Really at Odds with Molecules in Estimating Fern Phylogeny? |journal=[[Systematic Botany]] |date=1 July 2009 |volume=34 |issue=3 |pages=455–475 |doi=10.1600/036364409789271209 |s2cid=85855934 |ref={{harvid|Schneider et al|2009}}}}
* {{Cite thesis |last=Schuettpelz |first=Eric |title=The evolution and diversification of epiphytic ferns |url=http://dukespace.lib.duke.edu/dspace/bitstream/10161/181/1/D_Schuettpelz_Eric_a_052007.pdf |year=2007 |publisher=[[Duke University]] |type=[[PhD thesis]] |contribution=Table 1 |access-date=11 December 2009 |archive-date=20 June 2010 |archive-url=https://web.archive.org/web/20100620022844/http://dukespace.lib.duke.edu/dspace/bitstream/10161/181/1/D_Schuettpelz_Eric_a_052007.pdf |url-status=dead}}
* {{cite journal |last1=Schuettpelz |first1=Eric |last2=Rouhan |first2=Germinal |last3=Pryer |first3=Kathleen M. |last4=Rothfels |first4=Carl J. |last5=Prado |first5=Jefferson |last6=Sundue |first6=Michael A. |last7=Windham |first7=Michael D. |last8=Moran |first8=Robbin C. |last9=Smith |first9=Alan R. |title=Are there too many fern genera? |journal=[[Taxon (journal)|Taxon]] |date=1 June 2018 |volume=67 |issue=3 |pages=473–480 |doi=10.12705/673.1 |ref={{harvid|Schuettpelz et al|2018}} |doi-access=free}}
* {{cite journal |last=Smith |first=Alan R. |author2=Kathleen M. Pryer |author3=Eric Schuettpelz |author4=Petra Korall |author5=Harald Schneider |author6=Paul G. Wolf |year=2006 |title=A classification for extant ferns |url=https://www.idigbio.org/wiki/images/9/95/Smith_et_al_2006.pdf |journal=[[Taxon (journal)|Taxon]] |volume=55 |issue=3 |pages=705–731 |doi=10.2307/25065646 |jstor=25065646 |ref={{harvid|Smith et al.2006}}}}
* {{cite journal |last1=Stein |first1=W. E. |last2=Mannolini |first2=F. |last3=Hernick |first3=L. V. |last4=Landling |first4=E. |last5=Berry |first5=C. M. |year=2007 |title=Giant cladoxylopsid trees resolve the enigma of the Earth's earliest forest stumps at Gilboa |journal=[[Nature (journal)|Nature]] |volume=446 |issue=7138 |pages=904–907 |doi=10.1038/nature05705 |pmid=17443185 |bibcode=2007Natur.446..904S |s2cid=2575688 |ref={{harvid|Stein et al|2007}}}}
* {{cite journal |author=Walkowiak |first=Radoslaw Janusz |title=Classification of Pteridophytes – Short classification of the ferns. |journal=IEA Paper |date=2017 |url=https://internationalequisetologicalassociation.yolasite.com/resources/Classification%20of%20Pteridophytes.pdf |doi=10.13140/RG.2.2.29934.20809}}
* {{cite journal |last1=Underwood |first1=L. M. |title=The early writers on ferns and their collections. I. Linnaeus, 1707–1778 |journal=[[Torrey Botanical Society|Torreya]] |date=1903 |volume=3 |issue=10 |pages=145–150 |jstor=40594126 |issn=0096-3844}}

=== Websites ===

* {{cite web |last1=McCausland |first1=Jim |title=Rediscover ferns |url=https://www.sunset.com/garden/flowers-plants/rediscover-ferns |website=Garden plants |publisher=Sunset Magazine |access-date=22 November 2019 |date=22 February 2019 |archive-date=30 October 2021 |archive-url=https://web.archive.org/web/20211030104351/https://www.sunset.com/garden/flowers-plants/rediscover-ferns |url-status=dead}}
* {{cite web |title=Pteridopsida: Fossil Record |url=http://www.ucmp.berkeley.edu/plants/pterophyta/pteridofr.html |website=Plants: Pteridopsida |publisher=[[University of California Museum of Paleontology]] |access-date=23 November 2019 |ref={{harvid|UCMP|2019}}}}
* {{cite web |title=Classifying and identifying ferns |url=https://www.sciencelearn.org.nz/resources/1104-classifying-and-identifying-ferns |website=Science Learning Hub |publisher=[[The University of Waikato]] |access-date=24 November 2019 |language=en |date=3 September 2018 |ref={{harvid|SLH|2018}}}}
* {{cite encyclopedia |last1=Mickel |first1=John T. |last2=Wagner |first2=Warren H. |last3=Gifford |first3=Ernest M. |display-authors=etal |title=Fern |url=https://www.britannica.com/plant/fern |encyclopedia=[[Encyclopædia Britannica]] |access-date=24 November 2019 |date=4 February 2019 |ref={{harvid|EB|2019}}}} 
* {{cite web |last1=Hassler |first1=Michael |last2=Schmitt |first2=Bernd |title=Checklist of Ferns and Lycophytes of the World |url=https://worldplants.webarchiv.kit.edu/ferns/ |website=World Ferns |publisher=[[Botanical Garden of the Karlsruhe Institute of Technology]] |access-date=25 November 2019 |date=2 November 2019 |archive-date=2 September 2017 |archive-url=https://web.archive.org/web/20170902225743/http://worldplants.webarchiv.kit.edu/ferns/ |url-status=dead}}
* {{cite web |last1=Pryer |first1=Kathleen M. |last2=Smith |first2=Alan R. |last3=Rothfels |first3=Carl |title=Polypodiopsida |url=http://tolweb.org/Polypodiopsida/20615 |website=[[Tree of Life]] |date=2009 |ref={{harvid|Pryer et al|2006}}}}
* [https://web.archive.org/web/20160304060354/http://www.anbg.gov.au/fern/taxa/classification.html ''A classification of the ferns and their allies''.] (Australian National Herbarium)
* [https://web.archive.org/web/20160117055319/http://www.jaknouse.athens.oh.us/ferns/bookfern.html ''A fern book bibliography''.]
* [https://web.archive.org/web/20080509142839/http://www1.akira.ne.jp/~unzen/pteridophyta.html Register of fossil Pteridophyta]
* [http://delta-intkey.com/britfe/ Watson, L. and M. J. Dallwitz (2004 onwards). ''The Ferns (Filicopsida) of the British Isles''.] {{Webarchive|url=https://web.archive.org/web/20160303183034/http://delta-intkey.com/britfe/ |date=3 March 2016 }}
* [http://www.peterboyd.com/pteridomania2.htm ''Ferns and Pteridomania in Victorian Scotland''.]
* [https://web.archive.org/web/20120512162340/http://www.cas.vanderbilt.edu/bioimages/pages/non-seed-plants.htm Non-seed plant images at ''bioimages.vanderbilt.edu'']
* [http://www.amerfernsoc.org/ American Fern Society]
* [http://www.eBPS.org.uk/ British Pteridological Society]
* [http://internationalequisetologicalassociation.yolasite.com/ International Equisetological Association]
{{Refend}}

{{Botany}}
{{Plant classification}}
{{Fern classification}}
{{Taxonbar|from=Q98522578}}
{{Authority control}}

[[Category:Ferns| ]]
[[Category:Fern florae| ]]
[[Category:Non-timber forest products]]
[[Category:Extant Late Devonian first appearances]]