|Polypodiopsida/Pteridopsida ~ Modern Ferns|
Leptosporangiate ferns are the largest group of living ferns, including some 11000 species worldwide. They constitute the subclass Polypodiidae, but are often considered to be the class Pteridopsida or Polypodiopsida, although other classifications assign them a different rank. The leptosporangiate ferns are one of the four major groups of ferns, with the other three being the Eusporangiate ferns comprising the marattioid ferns (Marattiidae, Marattiaceae), the horsetails (Equisetiidae, Equisetaceae), and whisk ferns and moonworts.
There are approximately 8465 species of living leptosporangiate ferns, compared with about 2070 for all other ferns, totalling 10535 species of ferns. Almost a third of leptosporangiate fern species are epiphytes.
These ferns are called leptosporangiate because their sporangia arise from a single epidermal cell and not from a group of cells as in eusporangiate ferns (a polyphyletic lineage). The sporangia are typically covered with a scale called the indusium, which can cover the whole sorus, forming a ring or cup around the sorus, or can also be strongly reduced to completely absent. Many leptosporangiate ferns have an annulus around the sporangium, which ejects the spores.
Leptosporangiates include the vast majority of extant ferns. Only groups that branched off early from the fern lineage, which retain a eusporangium, are not included. Multiple attempts have been made to classify ferns. The classification scheme proposed by Smith et al. 2006 is the most widely accepted. More recent analyses by and Christenhusz et al. 2011  and Christenhusz & Chase 2014  offer additional insight into the group.
- Order Osmundales (royal ferns)
- Family Osmundaceae (4 genera, ca 25 species)
- Order Hymenophyllales (filmy ferns and bristle ferns)
- Family Hymenophyllaceae (2 genera, ca 650 species)
- Order Gleicheniales
- Order Schizaeales
- Order Salviniales
- Order Cyatheales
- Order Polypodiales
- Family Cystodiaceae (a single species, Cystodium sorbifolium)
- Family Lonchitidaceae (1 genus, 2 species)
- Family Lindsaeaceae (6 genera, ca 220 species)
- Family Saccolomataceae (2 genera, ca 12 species)
- Family Dennstaedtiaceae (incl. Hypolepidaceae, Monachosoraceae, Pteridiaceae) (10 genera, ca 240 species)
- Family Pteridaceae (incl. Acrostichaceae, Actiniopteridaceae, Adiantaceae, Anopteraceae, Antrophyaceae, Ceratopteridaceae, Cheilanthaceae, Cryptogrammaceae, Hemionitidaceae, Negripteridaceae, Parkeriaceae, Platyzomataceae, Sinopteridaceae, Taenitidaceae, Vittariaceae) (ca 44 genera, ca 1150 species)
- Family Aspleniaceae sensu lato (formerly eupolypods II, Blechnales, Athyriales, Aspleniales, or Thelypteridales) (ca 22 genera, ca 2780 species)
- Subfamily Cystopteridoideae, formerly Cystopteridaceae
- Subfamily Rhachidosoroideae, formerly Rhachidosoraceae
- Subfamily Diplaziopsidoideae, formerly Diplaziopsidaceae
- Subfamily Asplenioideae, formerly Aspleniaceae sensu stricto (incl. Hemidictyaceae)
- Subfamily Thelypteridoideae, formerly Thelypteridaceae
- Subfamily Woodsioideae, formerly Woodsiaceae
- Subfamily Blechnoideae, formerly Blechnaceae (incl. Onocleaceae, Stenochlaenaceae)
- Subfamily Athyrioideae, formerly Athyriaceae
- Family Polypodiaceae sensu lato (formerly eupolypods I
- Subfamily Didymochlaenoideae
- Subfamily Hypodematioideae, formerly Hypodematiaceae
- Subfamily Dryopteridoideae, formerly Dryopteridaceae (incl. Aspidiaceae, Bolbitidaceae, Elaphoglossaceae, Peranemataceae)
- Subfamily Lomariopsidoideae, formerly Lomariopsidaceae (incl. Nephrolepidaceae)
- Subfamily Tectarioideae, formerly Tectariaceae
- Subfamily Oleandroideae, formerly Oleandraceae
- subfamily Davallioideae, formerly Davalliaceae
- subfamily Polypodioideae sensu stricto, formerly Polypodiaceae sensu stricto (incl. Drynariaceae, Grammitidaceae, Gymnogrammitidaceae, Loxogrammaceae, Platyceriaceae, Pleurisoriopsidaceae)
The following phylogram shows a likely relationship between the other vascular plant classes and the leptosporangiate ferns. It was formerly unclear about the relationship between Equisetopsida, Psilotopsida, and Marattiopsida, but recent studies have shown that Equisetopsida is most likely sister to Psilotopsida.
Discussion of Molecular Classification
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. 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. 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 
- Palmer, Jeffrey (2004). "THE PLANT TREE OF LIFE: AN OVERVIEW AND SOME POINTS OF VIEW" (PDF). American Journal of Botany 91 (10): 1440. doi:10.3732/ajb.91.10.1437.
- Christenhusz, M.J.M.; Chase, M.W. (2014). "Trends and concepts of fern classification". Annals of Botany 113 (4): 571–594. doi:10.1093/aob/mct299. Retrieved 17 July 2014.
- Christenhusz, M.J.M., Zhang, X.C. & Schneider, H. (2011). "A linear sequence of extant families and genera of lycophytes and ferns" Phytotaxa 19: 5-22
- Smith, A. R., K. M. Pryer, et al. (2006). "A classification for extant ferns." Taxon 55(3): 705-731
- Chase, Mark W. and Reveal, James L. (October 2009), A phylogenetic classification of the land plants to accompany APG III 161 (2), Botanical Journal of the Linnean Society, pp. 122–127, doi:10.1111/j.1095-8339.2009.01002.x
- Schuettpelz, Eric. "Fern Phylogeny Inferred from 400 Leptosporangiate Species and Three Plastid Genes," contained in "The Evolution and Diversification of Epiphytic Ferns." Doctoral dissertation, Duke University. 2007. http://dukespace.lib.duke.edu/dspace/bitstream/10161/181/1/D_Schuettpelz_Eric_a_052007.pdf
- Christenhusz, M.J.M. (2009). "New combinations and an overview of Cyathea subg. Hymenophyllopsis (Cyatheaceae)" Phytotaxa 1: 37-42
- Samuli Lehtonen (2011). "Towards Resolving the Complete Fern Tree of Life" (PDF). PLoS ONE 6 (10): e24851. doi:10.1371/journal.pone.0024851. PMC 3192703. PMID 22022365.
- Hardeep S. Rai & Sean W. Graham (2010). "Utility of a large, multigene plastid data set in inferring higher-order relationships in ferns and relatives (Monilophytes)" (PDF). American Journal of Botany 97 (9): 1444–1456. doi:10.3732/ajb.0900305.
- Kathleen M. Pryer & Eric Schuettpelz (2009). "Ferns" (PDF). In S. Blair Hedges & Sudhir Kumar. The Timetree of Life. Oxford Biology.
- Rothwell, G. W. and K. C. Nixon (2006). "How does the inclusion of fossil data change our conclusions about the phylogenetic history of euphyllophytes." Int. J. Plant Sci 167(3): 737-749
- Kramer, K. U. (1990). Notes on the Higher Level Classification of the Recent Ferns. The Families and Genera of Vascular Plants: Pteridophytes and Gymnosperms. K. Kubitzki, K. U. Kramer and P. S. Green. New York, Springer-Verlag. 1: 49-52
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