Leptosporangiate fern
Pteridium aquilinum
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Division:	Polypodiophyta
Class:	Polypodiopsida
Subclass:	Polypodiidae Cronquist, Takht. & W.Zimm.[1]
Orders
Osmundales Hymenophyllales Gleicheniales Schizaeales Salviniales Cyatheales Polypodiales

ThePolypodiidae, commonly calledleptosporangiate ferns, formerlyLeptosporangiatae, are one of foursubclasses offerns, the largest of these being the largest group of living ferns, including some 11,000 species worldwide.^[2][3][4] The group has also been treated as the classPteridopsida or Polypodiopsida,^[5] although other classifications assign them a different rank.^[6] Older names for the group includeFilicidae andFilicales, although at least the "water ferns" (now theSalviniales) were then treated separately.

The leptosporangiate ferns are one of the four major groups of ferns, with the other three being theeusporangiate ferns comprising the marattioid ferns (Marattiidae,Marattiaceae), thehorsetails (Equisetiidae,Equisetaceae), andwhisk ferns andmoonworts.^[4][5] There are approximately 8465 species of living leptosporangiate ferns, compared with about 2070 for all other ferns, totalling 10535 species of ferns.^[3] Almost a third of leptosporangiate fern species areepiphytes.^[7]

These ferns are calledleptosporangiate because theirsporangia arise from a single epidermal cell and not from a group of cells as in eusporangiate ferns (a polyphyletic lineage). The mature sporangia have a wall that is just a single cell thick,^[8] and are typically covered with a scale called theindusium, which can cover the wholesorus, forming a ring or cup around the sorus, or can also be strongly reduced to completely absent. Many leptosporangiate ferns have anannulus around the sporangium, which ejects the spores.^[9]

The leptosporangiate ferns were first recognized as a group, the "Leptosporangiateen", byKarl Ritter von Goebel in 1881, who placed the eusporangiate ferns with seed plants and vascular plants into a coeval "Eusporangiateen". As this classification artificially split the ferns,Christian Luerssen subdivided thehomosporous ferns only into Eusporangiatae and Leptosporangiatae in 1884–9. The latter group was treated at a variety of ranks in subsequent systems of classification. The subclass "Polypodiidae" was first published and used for the homosporous leptosporangiate ferns by Cronquist, Takhtajan and Zimmermann in 1966, typified onPolypodiumL.. Other contemporary classifications used the name "Filicidae" for this subclass.^[10]

Smith et al. (2006) carried out the first higher-level classification of ferns based onmolecular phylogenetics. They includedheterosporous water ferns (Salviniales) (placed in a separate subclass by Cronquist et al. due to their highly modified morphology) within the leptosporangiate ferns, which they elevated to the rank of class as thePolypodiopsida (published by Cronquist et al. to include all ferns).^[5]

The common ancestor of Salviniales, Cyatheales and Polypodiales went through awhole genome duplication.^[11]

Later classifications renamed the group Polypodiidae, initially as a subclass ofEquisetopsidasensu lato.^[6] This subclass comprises leptosporangiate ferns as opposed to the remaining three subclasses which are informally referred to aseusporangiate ferns. The following diagram shows a likely phylogenic relationship between subclass Polypodiidae and the other Equisetopsida subclasses in that system^[4]

In 2014, Christenhusz andChase grouped all the fern subclasses together as Polypodiophyta^[3] and in 2016 the Pteridophyte Phylogeny Group (PPG) adopted the class Polypodiopsidasensu lato for the four fern subclasses. The followingcladogram shows the phylogenic relationship between the subclasses according to the PPG. The first three small subclasses being informally grouped aseusporangiate ferns, in contrast to the Polypodiidae or leptosporangiate ferns. Polypodiidae is shown as asister group of Marattiidae.^[1]

In both the Christenhusz and Chase, and the PPG classification, the extant Polypodiidae are divided into seven orders, 44 families, 300 genera, and an estimated 10,323 species.^[1][3]

The following phylogram shows a likely relationship between the other vascular plant classes and the leptosporangiate ferns. It was formerly unclear about the relationship betweenEquisetopsida,Psilotopsida, andMarattiopsida,^[14][15][16] but recent studies have shown that Equisetopsida is most likely sister to Psilotopsida.

There has been some challenge to recent molecular studies, claiming that these provide a skewed view of the phylogenetic order because they do not take into account fossil representatives.^[17] However, the molecular studies have clarified relations among families that had already been thought to be polyphyletic before the advent of molecular information but that were left in their polyphyletic ranks because there was not enough information to do otherwise.^[18] The classification of ferns using these molecular studies, which have generally supported one another, reflects the best information available at present, because traditional morphological characters are not always informative in elucidating evolutionary relationships among ferns.^[3]

The leptosporangiate ferns have a substantial fossil record. For example, fossils assigned to theDicksoniaceae, a member of the Cyatheales, are known from theLower Jurassic (201 to 175 million years ago).^[19] A number of other extinct families have been described. They are not included in the classification systems used for extant ferns, and so most cannot be assigned to orders used in these systems. Taylor et al. (2009) use the order "Filicales", which corresponds to four Polypodiidae orders in more modern systems: Hymenophyllales, Gleicheniales, Schizaeales and Cyatheales. The unplaced families include:^[20]

• Anachoropteridaceae
• Botryopteridaceae
• Kaplanopteridaceae
• Psalixochlaenaceae
• Sermayaceae
• Skaaripteridaceae
• Tedeleaceae
• Tempskyaceae

• Polypodiidae
• Plant classes

• Articles with short description
• Short description is different from Wikidata
• Articles with 'species' microformats
• Taxonbars with multiple manual Wikidata items