Editing Fern (section)

=== 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]]
|}