Editing Lycopodiopsida (section)

==Taxonomy==
===Phylogeny===
The extant lycophytes are [[vascular plant]]s (tracheophytes) with [[Microphylls and megaphylls|microphyllous leaves]], distinguishing them from the [[euphyllophyte]]s (plants with [[Microphylls and megaphylls|megaphyllous leaves]]). The sister group of the extant lycophytes and their closest extinct relatives are generally believed to be the [[zosterophyll]]s, a [[Paraphyly|paraphyletic]] or [[plesion]] group. Ignoring some smaller extinct taxa, the evolutionary relationships are as shown below.<ref name=KenrCran97a/><ref name=Maus14/><ref name=PPGI/>
{{clade
|label1=[[Vascular plant|tracheophytes]]
|sublabel1=&thinsp;(vascular plants)&thinsp;
|1={{clade
   |label1=lycophytes
   |sublabel1=&thinsp;(broadly defined)&thinsp;
   |1={{clade
      |label1=†[[zosterophyll]]s 
      |1=&thinsp;(multiple branches, ''[[incertae sedis]]'')
      |state1=double
      |label2='''lycopodiopsida'''
      |2=&thinsp;living lycophytes and<br/>&thinsp;their extinct close relatives 
      }}
   |label2=[[euphyllophyte]]s 
   |2={{clade
      |1=&thinsp;[[fern]]s & [[Equisetales|horsetail]]s
      |2=&thinsp;[[spermatophyte]]s<br/>&thinsp;(seed plants)
      }}
   }}
}}
{{As of|2019}}, there was broad agreement, supported by both molecular and morphological evidence, that the extant lycophytes fell into three groups, treated as orders in PPG&nbsp;I, and that these, both together and individually, are [[Monophyly|monophyletic]], being related as shown in the cladogram below:<ref name=PPGI/>
{{clade
|label1=&thinsp;extant lycophytes&thinsp;
|1={{clade
   |1=&thinsp;[[Lycopodiales]]&thinsp;
   |2={{clade
      |1=&thinsp;[[Isoetales]]
      |2=&thinsp;[[Selaginellales]]
      }}
   }}
}}

===Classification===
The rank and name used for the taxon holding the extant lycophytes (and their closest extinct relatives) varies widely. Table 1 below shows some of the highest ranks that have been used. Systems may use taxa at a rank lower than the highest given in the table with the same circumscription; for example, a system that uses Lycopodiophyta as the highest ranked taxon may place all of its members in a single subclass.
{{anchor|Table 1}}
{| class="wikitable"
|+ Table 1: Alternative highest ranks used which include only extant species and their closest relatives
|-
! Highest rank !! Name !! Example sources
|-
| Division (phylum)|| Lycophyta || Taylor et al. (2009),<ref name=TaylTaylKrin09/> Mauseth (2014)<ref name=Maus14/>
|-
| Division (phylum) || Lycopodiophyta || Niklas (2016)<ref name=Nikl16/>
|-
| Subdivision (subphylum)|| Lycopodiophytina || Ruggiero et al. (2015)<ref name=RuggGordOrreBail15/>
|-
| Class || Lycopsida || Kenrick & Crane (1997)<ref name=KenrCran97a/><ref name=KenrCran97b/>
|-
| '''Class''' || '''Lycopodiopsida''' || PPG I (2016)<ref name=PPGI/>
|-
| Subclass || Lycopodiidae || Chase & Reveal (2009)<ref name=ChasReve09/>
|}

Some systems use a higher rank for a more broadly defined taxon of lycophytes that includes some extinct groups more distantly related to extant lycophytes, such as the [[zosterophyll]]s. For example, Kenrick & Crane (1997) use the subdivision Lycophytina for this purpose, with all extant lycophytes falling within the class Lycopsida.<ref name=KenrCran97a/> Other sources exclude the zosterophylls from any "lycophyte" taxon.<ref name=TaylTaylKrin09/>

In the [[Pteridophyte Phylogeny Group]] classification of 2016 (PPG I), the three orders are placed in a single class, Lycopodiopsida, holding all extant lycophyte species. Older systems have used either three classes, one for each order, or two classes, recognizing the closer relationship between Isoetales and Selaginellales. In these cases, a higher ranked taxon is needed to contain the classes (see Table 1). As Table 2 shows, the names "Lycopodiopsida" and "Isoetopsida" are both ambiguous.
{{anchor|Table 2}}
{| class="wikitable"
|+ Table 2: Alternative arrangements of the orders of extant lycophytes into classes
|-
! Order || 3 classes<br/>e.g. ''IUCN Red List'', 2004<ref name=BailHiltStua04/> || 2 classes<br/>e.g. Yatsentyuk et al. (2001)<ref name=Yats01/> || 1 class<br/>PPG I<ref name=PPGI/>
|-
| Lycopodiales || Lycopodiopsida || Lycopodiopsida ||rowspan=3|Lycopodiopsida
|-
| Isoetales || |Isoetopsida ||rowspan=2|Isoetopsida
|-
| Selaginellales || Sellaginellopsida
|}

===Subdivisions===
The PPG I system divides up the extant lycophytes as shown below.
*Class Lycopodiopsida <small>Bartl.</small> (3 orders)
:*Order [[Lycopodiales]] <small>DC. ex Bercht. & J.Presl</small> (1 extant family)
::*Family [[Lycopodiaceae]] <small>P.Beauv.</small> (16 extant genera)
:*Order [[Isoetales]] <small>Prantl</small> (1 extant family)
::*Family [[Isoetaceae]] <small>Dumort.</small> (1 extant genus)
:*Order [[Selaginellales]] <small>Prantl</small> (1 extant family)
::*Family [[Selaginellaceae]] <small>Willk</small> (1 extant genus)

Some extinct groups, such as [[zosterophyll]]s, fall outside the limits of the taxon as defined by the classifications in Table 1 above. However, other extinct groups fall within some [[Circumscription (taxonomy)|circumscriptions]] of this taxon. Taylor et al. (2009) and Mauseth (2014) include a number of extinct orders in their division (phylum) Lycophyta, although they differ on the placement of some genera.<ref name=TaylTaylKrin09/><ref name=Maus14/> The orders included by Taylor et al. are:<ref name=TaylTaylKrin09/>
*Order †[[Drepanophycales]] (including ''[[Baragwanathia]]'', ''[[Drepanophycus]]'' and ''[[Asteroxylon]]'')
*Order †[[Protolepidodendrales]]
*Order †[[Lepidodendrales]]
*Order †[[Pleuromeiales]]
Mauseth uses the order †Asteroxylales, placing ''Baragwanathia'' in the Protolepidodendrales.<ref name=Maus14/>

The relationship between some of these extinct groups and the extant ones was investigated by Kenrick and Crane in 1997. When the genera they used are assigned to orders, their suggested relationship is:{{sfnp|Kenrick|Crane|1997a|p=239}}
{{clade
|1={{clade
   |1=†Drepanophycales (†''[[Asteroxylon]]'', †''[[Baragwanathia]]'', †''[[Drepanophycus]]'')
   |2={{clade
      |1=Lycopodiales
      |2={{clade
         |1=†Protolepidodendrales (†''[[Leclercqia (plant)|Leclercqia]]'', †''[[Minarodendron]]'')
         |2={{clade
            |1=Selaginellales (''[[Selaginella]]'', including subg. ''Stachygynandrum'' and subg. ''Tetragonostachys'')
            |2={{clade
               |1=Isoetales (''[[Isoetes]]'')
               |2=†Lepidodendrales (†''[[Paralycopodites]]'')
               }}
            }}
         }}
      }}
   }}
}}