| Polypodiales | |
|---|---|
 | |
| Polypodium californicum | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Division: | Polypodiophyta |
| Class: | Polypodiopsida |
| Subclass: | Polypodiidae |
| Order: | Polypodiales Link (1833) |
| Suborders[2] | |
6.See text | |
TheorderPolypodiales encompasses the major lineages of polypodferns, which comprise more than 80% of today's fern species. They are found in many parts of the world includingtropical,semitropical andtemperate areas.
Polypodiales are unique in bearingsporangia with a verticalannulus interrupted by the stalk andstomium.[3] These sporangial characters were used byJohann Jakob Bernhardi to define a group of ferns he called the "Cathetogyratae";[4] the Pteridophyte Phylogeny Group has suggested reviving this name as the informal termcathetogyrates, to replace the ambiguously circumscribed term "polypods" when referring to the Polypodiales.[2] The sporangia are born on stalks 1–3 cells thick and are often long-stalked.[3] (In contrast, theHymenophyllales have a stalk composed of four rows of cells.)[5] The sporangia do not reach maturity simultaneously. Many groups in the order lackindusia, but when present, they are attached either along the edge of the indusium or in its center.[3]
Both Polypodiales and Cyatheales differ from other ferns in having a photoreceptor called a neochrome, which allows them to perform photosynthesis better in low-light conditions, such as in the shadows on the forest floor. The common ancestor of the two groups appears to have derived the neochrome viahorizontal gene transfer from ahornwort.[6]
Theirgametophytes are green, usually heart-shaped, and grow at the surface[3] (rather than underground, as inOphioglossales).[7]
The order Polypodiales was first described byLink in 1833.[2] Thecircumscription of the order has changed over time asferns have been classified in many different ways (see the review byChristenhusz andChase, 2014).[8] Smith et al. (2006) carried out the first higher-levelpteridophyte classification published in themolecular phylogenetic era.[9] They referred to the ferns (now including horsetails) as monilophytes, dividing them into four groups, with the vast majority of species being placed in a taxon they called "Polypodiopsida". The four-fold grouping has persisted through subsequent systems, despite changes in nomenclature.[10][11][8][2]Polypodiopsida is now used for all ferns (sensu lato),[2] with Smith et al.'s group being subclassPolypodiidae. This group, which includes Polypodiales, is also informally known as theleptosporangiate ferns, while the remaining three groups (subclasses) are referred to aseusporangiate ferns. The Polypodiidae have been divided into sevenorders, Polypodiales being the largest. Thephylogenetic position of Polypodiales in relation to the other orders of Polypodiidae is shown in the followingcladogram.[2]
| Subclass Polypodiidae |
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Despite being the most diverse order of ferns, they appeared relatively late in the evolutionary history of the group, during the Early Cretaceous, and diversified substantially throughout the period.[12]
The division of the Polypodiales into families has changed somewhat between the pioneering work of Smith et al. (2006) and the Pteridophyte Phylogeny Group's classification of 2016, with a general increase in the number of divisions recognized, albeit sometimes at different ranks. The table below summarizes four systems; families are listed alphabetically within three broad groups. Although the same families are used in more than one system, circumscriptions may differ. Christenhusz and Chase in 2014 used a very broad circumscription of Aspleniaceae and Polypodiaceae, reducing families used in other systems to subfamilies.
| Smith et al. (2006)[9] | Christenhusz et al. (2011)[11] | Christenhusz & Chase (2014)[8] | PPG I (2016)[2] | |
|---|---|---|---|---|
| Basal families | – | Cystodiaceae | Cystodiaceae | Cystodiaceae |
| Dennstaedtiaceae | Dennstaedtiaceae | Dennstaedtiaceae | Dennstaedtiaceae | |
| Lindsaeaceae | Lindsaeaceae | Lindsaeaceae | Lindsaeaceae | |
| – | Lonchitidaceae | Lonchitidaceae | Lonchitidaceae | |
| Pteridaceae | Pteridaceae | Pteridaceae | Pteridaceae | |
| Saccolomataceae | Saccolomataceae | Saccolomataceae | Saccolomataceae | |
| Aspleniineae eupolypods II (Aspleniaceae) | Aspleniaceae | Aspleniaceae | Aspleniaceae: Asplenioideae | Aspleniaceae |
| – | Athyriaceae | Aspleniaceae: Athyrioideae | Athyriaceae | |
| Blechnaceae | Blechnaceae | Aspleniaceae: Blechnoideae | Blechnaceae | |
| – | Cystopteridaceae | Aspleniaceae: Cystopteridoideae | Cystopteridaceae | |
| – | – | – | Desmophlebiaceae | |
| – | Diplaziopsidaceae | Aspleniaceae: Diplaziopsidoideae | Diplaziopsidaceae | |
| – | – | – | Hemidictyaceae | |
| Onocleaceae | Onocleaceae | – | Onocleaceae | |
| – | Rhachidosoraceae | Aspleniaceae: Rhachidosoroideae | Rhachidosoraceae | |
| Thelypteridaceae | Thelypteridaceae | Aspleniaceae: Thelypteridoideae | Thelypteridaceae | |
| Woodsiaceae | Woodsiaceae | Aspleniaceae: Woodsioideae | Woodsiaceae | |
| Polypodiineae eupolypods I (Polypodiaceae) | Davalliaceae | Davalliaceae | Polypodiaceae: Davallioideae | Davalliaceae |
| – | – | Polypodiaceae: Didymochlaenoideae | Didymochlaenaceae | |
| Dryopteridaceae | Dryopteridaceae | Polypodiaceae: Dryopteridoideae | Dryopteridaceae | |
| – | Hypodematiaceae | Polypodiaceae: Hypodematioideae | Hypodematiaceae | |
| Lomariopsidaceae | Lomariopsidaceae | Polypodiaceae: Lomariopsidoideae | Lomariopsidaceae | |
| – | Nephrolepidaceae | – | Nephrolepidaceae | |
| Oleandraceae | Oleandraceae | Polypodiaceae: Oleandroideae | Oleandraceae | |
| Polypodiaceae | Polypodiaceae | Polypodiaceae: Polypodioideae | Polypodiaceae | |
| Tectariaceae | Tectariaceae | Polypodiaceae: Tectarioideae | Tectariaceae |
Smith et al. (2006) divided the Polypodiales into fifteen families,[9] a practice continued in their 2008 revision,[13] with members of the eupolypods placed in two unranked clades. The families are listed in the table. While many of these families had previously been recognized with similar circumscriptions, the authors noted that Dryopteridaceae was more narrowly bounded than in historical circumscriptions, which had included their Tectariaceae, Onocleaceae and Woodsiaceae. The circumscription of Lomariopsidaceae changed dramatically, with most historical genera of that family (exceptLomariopsis andThysanosoria) being moved to Dryopteridaceae, whileCyclopeltis andNephrolepis were added. Saccolomataceae were removed from the dennstaedtioids.Cystodium was tentatively placed inLindsaeaceae, away from its historical position with thetree ferns. Woodsiaceae was acknowledged to be of uncertain circumscription and perhaps paraphyletic; the inclusion ofHypodematium,Didymochlaena, andLeucostegia perhaps also rendering Dryopteridaceae paraphyletic. Thegrammitids were included inPolypodiaceae to render that family monophyletic.[9]
The linear sequence ofChristenhusz et al. (2011), intended for compatibility with the classification of Chase and Reveal (2009),[10] incorporated new phylogenetic evidence to make several changes at the familial level, resulting in an expansion to 23 families.Lonchitis andCystodium were removed from the Lindsaeaceae and incorporated into new families,Lonchitidaceae andCystodiaceae respectively. Within eupolypods I, Woodsiaceae proved to be paraphyletic and was reduced to the generaCheilanthopsis,Hymenocystis, andWoodsia, while the remainder of its genera were removed toCystopteridaceae,Diplaziopsidaceae,Rhachidosoraceae,Athyriaceae, andHemidictyaceae. Within eupolypods II,Nephrolepis was placed in a new family, theNephrolepidaceae, due to uncertainty in its phylogenetic placement, whileHypodematiaceae was split from Dryopteridaceae to contain the three problematic genera mentioned by Smith et al.[11]
The classification of Christenhusz and Chase (2014) dramatically reduced the number of families recognized in this order to eight by "lumping", reducing many families to subfamilies and expanding the circumscription of Polypodiaceae and Aspleniaceae to encompass all ofeupolypods I andeupolypods II, respectively. Former families became subfamilies (see the table above). The former Hemidictyaceae were included in the Asplenioideae, and the Onocleaceae in the Blechnoideae. In the new Polypodiaceae,Didymochlaena was placed in its own subfamily, Didymochlaenoideae.[8]
The PPG I classification (2016) used a process intermediate between the two previous approaches, by introducing a new rank, that of suborder, and organising 26 families (in some cases very narrowly circumscribed) into six suborders, largely returning to the families set out by Christenhusz et al. in 2011. In lieu of the expansion of Aspleniaceae and Polypodiaceae, eupolypods I and II were recognized and named as suborders:[2][8]
| Pteridophyte Phylogeny Group 2016[2] | Nitta et al. 2022[14] and Fern Tree of life[15] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Now-obsolete families of Polypodiales include:
Polypodiales may be regarded as one of the mostevolutionarily advanced orders of monilophytes (ferns), based on recent genetic analysis. They arose and diversified about 100 million years ago, probably subsequent to the diversification of theangiosperms.[16]
Classification ofArchaeplastida orPlantaes.l. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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