Pteridaceae are one of the largest fern families, comprising over 1000 species (~10% of extant ferns). But even more notable than their species richness is the remarkable morphological and ecological diversity of the family, which includes obligate epiphytes, free-floating aquatics, brackish-swamp dwellers, several clades specialized for colonizing rocky deserts, and many generalist understory species. While some of these life forms do appear in other fern lineages (many other families, for example, contain epiphytes), most are rare and no other fern family contains such a wide range of ecological specializations.
Pteridaceae have been the subject of much taxonomic disagreement—their members have been distributed among at least 20 different families: Acrostichaceae; Actiniopteridaceae; Adiantaceae; Anopteraceae; Antrophyaceae; Bommeriaceae; Ceratopteridaceae; Cheilanthaceae; Coniogrammaceae; Crytopgrammaceae; Hemionitidaceae; Llaveaceae; Negripteridaceae; Notholaenaceae; Parkeriaceae; Platyzomataceae; Pteridaceae; Sinopteridaceae; Taenitidaceae; and Vittariaceae (Smith et al. 1996; Hassler and Swale, 2003). Some of these former family designations (e.g., Llaveaceae, Parkeriaceae, and Vittariaceae) correspond to monophyletic groups now known to be nested within the broader Pteridaceae, while others (e.g., Taenitidaceae) are assemblages of more distantly related species (Schuettpelz et al., 2007).
"Pteroids" vs. "Pteridoids"
Note that the term “pteroid” is colloquial shorthand to refer to members of the Pteridaceae, whereas “pteridoid” refers to members of a specific Pteridaceae subclade.
Perhaps due to the group's ecological breadth, Pteridaceae lack clear, unique, morphological features that unite their constituent species. One of the best characteristics is that members of this family never have true indusia—outgrowths of the lower leaf surface that protect the sporangia—although they frequently have modified leaf edges that serve the same function. These recurved leaf margins are sometimes strongly differentiated from the rest of the leaf tissue, and are thus referred to as “false indusia.”
Left: Abaxial leaf surfaces of Adiantum poiretii, showing sori and false indusia. © 2008 Carl Rothfels. Center: Fertile sporophyte of Coniogramme sp., showing sporangia distributed along the veins on the underside of the leaf. © 2007 Michael Sundue. Right: Naked sporangia arranged along the veins of the leaf of Hemionitis palmata. © 2004 Robbin Moran
Instead of the round or elongate sori (clusters of sporangia) that are typical of many ferns, members of the Pteridaceae usually have their sporangia distributed along the veins on the underside of the leaf, often in marginal coenosori (a more-or-less contiguous line of sporangia around the margin of the leaf). More rarely, the sporangia may be attached to the false indusium itself (Adiantum), or spread evenly across the undersurface of the leaf (Acrostichum). In addition to these macromorphological characteristics, members of the Pteridaceae tend to share a chromosome base number of x=30 (occasionally x=27, 28, or 29).
Evolution and Systematics
Discussion of Phylogenetic Relationships
Plastid DNA sequence data suggest that the Pteridaceae comprise five (mostly) well-supported clades (Schuettpelz et al., 2007). The cheilanthoids are sister to the adiantoids (which include both Adiantum and the group formerly referred to as the Vittariaceae); these two clades are together sister to the pteridoids plus the ceratopteroids; and the cryptogrammoids are, in turn, sister to this large clade. Of these five clades, only the cheilanthoids lack strong support, due to some uncertainty about the phylogenetic position of their earliest-diverging branch (the Doryopteris ludens clade—see the cheilanthoid page). These five clades, none of which correspond perfectly with previously recognized families or subfamilies, do show some ecological differentiation. The ceratopteroids contain the aquatic taxa; the pteridoids contain most of the generalist forest understory species; and the cheilanthoids contain most of the xeric habitat specialists.
This phylogenetic structure differs from the most recent formal taxonomic treatments of the family (Kramer, 1990; Tryon et al., 1990), which recognized two families (Pteridaceae and Vittariaceae), and divided the Pteridaceae into six subfamilies: Adiantoideae, Ceratopteridoideae, Cheilanthoideae, Platyzomatoideae, Pteridoideae, and Taenitidoideae. Molecular data demonstrate that the Vittariaceae are nested within Pteridaceae (specifically within the adiantoid clade), and, while the circumscriptions may be close in some cases, none of the formally described subfamilies of Tryon and Tryon (1990; Adiantoideae, Cheilanthoideae, etc.) corresponds perfectly to the informal clades recognized here (adiantoids, cheilanthoids, etc.). A formal revision of Pteridaceae awaits further data.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimens with Sequences:671
Specimens with Barcodes:633
Species With Barcodes:252
Statistics of barcoding coverage
Specimens with Sequences:468
Specimens with Barcodes:462
Species With Barcodes:211
Pteridaceae is a large family of ferns in the order Polypodiales. Members of the family have creeping or erect rhizomes and are mostly terrestrial or epipetric (growing on rock). The leaves are almost always compound and have linear sori that are typically on the margins of the leaves and lack a true indusium, typically being protected by a false indusium formed from the reflexed margin of the leaf. The family includes four groups of genera that are sometimes recognized as separate families: the adiantoid, cheilanthoid, pteroid, and hemionitidoid ferns. Relationships among these groups remain unclear, and although some recent genetic analyses of the Pteridales suggest that neither the family Pteridaceae nor the major groups within it are all monophyletic, as yet these analyses are insufficiently comprehensive and robust to provide good support for a revision of the order at the family level.
As traditionally defined, the groups within Pteridaceae are as follows:
- Adiantoid ferns (tribe Adianteae Gaudich. 1829); epipetric, terrestrial or epiphytic in moist habitats, rachis often dichotomously branching; sori relatively small and discrete with sporangia born on the false indusium rather than the leaf blade proper; only one genus:
- Cheilanthoid ferns; primarily epipetric in semiarid habitats; leaves mostly with well-developed scales or trichomes, often bipinnate or otherwise highly compound; sporangia mostly born in marginal sori with false indusia that are +/- continuous around the leaf margins; several genera, including:
- Pteridoid ferns (tribe Pterideae J. Sm 1841); terrestrial and epipetric in moist habitats; leaves mostly without prominent scales or trichomes, most often pinnate but sometimes more compound; sporangia born in marginal sori with false indusia that are +/- continuous around the leaf margins; several genera, including:
- Parkerioid ferns (tribe Parkerieae Brongn. 1843); aquatic in swamps and/or mangroves, including:
- Hemionitidoid ferns; terrestrial, epipetric or epiphytic in moist or semiarid habitats; leaves simple, pinnate, or more compound; sporangia born in linear non-marginal, exindusiate sori or sometimes in marginal sori; several genera, including:
- Vittarioid ferns (tribe Vittarieae C. Presl 1836); primarily epiphytic in tropical regions and all have simple leaves with sori that follow the veins and lack true indusia:
Based on phylogenetic research, Christenhusz et al. (2011) divided the Pteridaceae genera into the following subfamilies. These roughly correspond with the groups listed above, with the main difference being that adiantoid and vittarioid ferns are combined under the Vittarioideae subfamily name.
- Cryptogrammoideae S.Linds. 2009
- Ceratopteridoideae (J.Sm.) R.M.Tryon 1986
- Pteridoideae C.Chr. ex Crabbe, Jermy & Mickel 1975
- Genera: Actiniopteris, Anogramma, Aspleniopsis, Austrogramme, Cerosora, Cosentinia, Jamesonia (incl. Eriosorus), Nephopteris, Onychium, Pityrogramma, Pteris (incl. Neurocallis & Platyzoma), Pterozonium, Syngramma, Taenitis
- Cheilanthoideae W.C.Shieh 1973
- Genera: Adiantopsis, Aleuritopteris, Argyrochosma, Aspidotis, Astrolepis, Bommeria, Calciphilopteris, Cassebeera, Cheilanthes, Cheiloplecton, Doryopteris, Hemionitis, Mildella, Notholaena, Paraceterach, Paragymnopteris, Pellaea, Pentagramma, Trachypteris, Tryonella
- Vittarioideae (C.Presl) Crabbe, Jermy & Mickel 1975
- Genera: Adiantum, Ananthacorus, Anetium, Antrophyum, Haplopteris, Hecistopteris, Monogramma, Polytaenium, Radiovittaria, Rheopteris, Scoliosorus, Vittaria
- "Family: Pteridaceae E. D. M. Kirchn.". Germplasm Resources Information Network. United States Department of Agriculture. 2001-08-14. Retrieved 2011-11-04.
- Christenhusz, Maarten J. M.; Zhang, Xian-Chun; Schneider, Harald (18 February 2011). "A linear sequence of extant families and genera of lycophytes and ferns". Phytotaxa 19: 7–54. ISSN 1179-3163.
- Adianteae Tropicos.org. Missouri Botanical Garden. 14 Jan 2012
- "Pteridaceae". Integrated Taxonomic Information System. Retrieved 2011-11-04.
- "GRIN Genera of Pteridaceae". Germplasm Resources Information Network. United States Department of Agriculture. Retrieved 2011-11-04.
- Pterideae Tropicos.org. Missouri Botanical Garden. 14 Jan 2012
- Parkerieae Tropicos.org. Missouri Botanical Garden. 14 Jan 2012
- Vittarieae Tropicos.org. Missouri Botanical Garden. 14 Jan 2012
- Schuettpelz & Pryer (2008) "Fern phylogeny" in Biology and Evolution of Ferns and Lycophytes, ed. Tom A. Ranker and Christopher H. Haufler. Cambridge University Press 2008
- Schuettpelz et al. (2007) Eric Schuettpelz, 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 (2007) 1172–1185
Although Ceratopteris was long isolated under its own family, due to adaptations for a dedicated aquatic existence, recent genetic study has determined that these two genera are allied.
The correct name for this taxon at the level of family is Parkeriaceae.
Christenhusz et al., 2011, included these two genera alone in the subfamily Ceratopteridoideae (the correct name at the level of subfamily) in their larger treatment of the Pteridaceae family in the order Polypodiales.
- Christenhusz et al., 2011 Maarten J. M. Christenhusz, Xian-Chun Zhang & Herald Scheider: "A linear sequence of extant families and genera of lycophytes and ferns," Phytotaxa, 19: 7-54 (18 Feb. 2011)
Adiantaceae (as construed here, sensu strictu, not a synonym of Pteridaceae) is a family of ferns in the order Pteridales. This includes the family formerly known as the "Vittariaceae." Recent genetic analyses based on chloroplast genes demonstrate that the vittarioid ferns cladistically nest within the genus Adiantum, making that genus paraphyletic.
The vittarioid ferns are primarily epiphytic in tropical regions and all have simple leaves with sori that follow the veins and lack true indusia; the sori are most often marginal with a false indusium formed from the reflexed leaf margin. The family also includes a species, Vittaria appalachiana, that is highly unusual in that the sporophyte stage of the life cycle is absent. This species consists solely of photosynthetic gametophytes that reproduce asexually.
The ferns historically considered as Adiantum include both petrophilic and terrestrial plants. Most of the species in this genus do compose a clade within the family, but apparently Adiantum raddianum and possibly some related species constitute a clade that is sister to the vittarioids combined with the rest of the genus Adiantum.
Based on phylogenetic research, Smith et al. (2006) included Adiantaceae as part of the family Pteridaceae and Christenhusz et al. (2011) listed its genera in Vittarioideae (C.Presl) Crabbe, Jermy & Mickel 1975, one of five subfamilies of Pteridaceae.
- Smith et al. (2006) A classification for extant ferns Taxon 55(3): 705–731 (Aug 2006)
- Christenhusz, Maarten J. M.; Zhang, Xian-Chun; Schneider, Harald (18 February 2011). "A linear sequence of extant families and genera of lycophytes and ferns". Phytotaxa 19: 7–54. ISSN 1179-3163. http://www.mapress.com/phytotaxa/content/2011/f/pt00019p054.pdf.
- 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
- Lindsay, Stuart (2003) Considerations for a revision of the fern family Vittariaceae for Flora Malesiana. Telopea 10(1) : 99-112.
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