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|Adiantum lunulatum in Goa, India.|
This order is considered a family under the Smith classification. However, this group, a natural clade, is clearly the most basal offshoot of the entire polypodioid line, and if any portion of that clade is segregated as a separate order, this would be the obvious one.[dubious ] For this reason, and because this is a large and complex group, it is being considered an order for this page.
One of the most well known plants in this order is the maidenhair fern Adiantum, with many forms in cultivation. Also commonly cultivated are various species of Pteris, sometimes known as "table ferns," and some species of Pellaea, including the button fern.
While this group has long been recognized as distinct from the rest of the polypodioid ferns, relationships within the group have long been misunderstood. A ground-breaking paper by Schuettpelz et al. has redefined this order using not only morphological data, but also extensive genetic data. The cladogram at left is based on their data. Line length in this diagram is not meaningful.
Cheilanthes, Pellaea, Doryopteris, Jamesonia, Anogramma, and Pteris have all been shown to be seriously paraphyletic genera. Jamesonia and Eriosorus were found to be a highly paraphyletic mixture, although in their own clade. More surprisingly, they found that the vittarioid ferns nest within the genus Adiantum. And they have established that Acrostichum and Ceratopteris are allied within their own isolated clade.
Deriving from the results of this important study, it is clear that the Pteridales should include five distinct families, although their final names are yet to be determined:
- Pellaeaceae (may also be named Sinopteridaceae or Cheilantheaceae): including most of the ferns long recognized as a natural grouping of largely xeric, petrophilic, frequently apogamous small ferns
- Adiantaceae (sensu strictu in comparison with past usage): including both rock and terrestrial plants, variously either delicately cut or grass-like
- Pteridaceae (sensu strictu): including most small to medium sized terrestrial plants
- Ceratopteridaceae (replacing Parkeriaceae which is an invalid name under current rules): exclusively wetland or aquatic ferns (Acrostichum and Ceratopteris)
- Cryptogrammaceae: largely rock plants, including Llavea, Coniogramme, and Cryptogramma
- A. R. Smith, K. M. Pryer, E. Schuettpelz, P. Korall, H. Schneider, P. G. Wolf. 2006. "A classification for extant ferns". Taxon 55(3), 705-731 (pdf here)
- Schuettpelz, Eric, Harald Schneider, Layne Huiet, Michael D. Windham, Kathleen M. Pryer. "A molecular phylogeny of the fern family Pteridaceae: Assessing overall relationships and the affinities of previously unsampled genera." Molecular Phylogenetics and Evolution, 44: 1172–1185. 2007: http://www.pryerlab.net/publication/fichier1047.pdf