Polypodiales

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The largest order of modern ferns, commonly called the true ferns, with approximately 250 genera and 9000 species; also known as Filicales. Although well represented in the temperate regions, they reach their greatest development in the moist tropics. They vary in habit from small filmy structures to large treelike plants. Many are epiphytic (live perched on other plants) and a number are climbing species. A few are aquatic. Perhaps the most striking species are the tropical tree ferns with their upright, unbranched stems and terminal clusters of large graceful leaves.

The Polypodiales differ from the other fem orders in being leptosporangiate—that is, their sporangium, or spore sac, arises from a single surface cell—and in having small sporangia with a definite number of spores. The wall of the sporangium is almost encircled with a ring of cells having unevenly thickened walls. This ring is called the annulus. When the sporangium is mature, the annulus, acting as a spring, causes the sporangium wall to rupture, thus discharging the spores. These plants are valued for their beauty and for the clues they give to the evolutionary history of the Polypodiales which extends back through the coal measures of the Paleozoic. See also Paleobotany.

The sporophyte is the conspicuous phase of the true ferns, and like other vascular plants it has true roots, stems, and leaves. In most ferns, especially those of the temperate regions, the mature stem is usually a creeping rhizome (underground stem) without aerial branches. However, in several species the stems are branched, and in some they are erect. Whereas in the tropics the leaves are usually persistent and evergreen, in temperate regions the leaves of most species die back each year and are replaced by new ones the next growing season. Characteristic of this order is the apparent uncoiling of the leaves from the base toward the apex.

The internal structure of the blade of the leaf and of the root is very similar to that of these organs in the seed plants. The main difference is the presence of large intercellular spaces in the fern leaf and the frequent lack of apparent distinction between the spongy and palisade cells of the mesophyll, possibly because most ferns grow in the shade.

The life cycle of the fern consists of two independent (self-sustaining) alternating generations. The common leafy fern plant is the sporophytic (spore-producing) generation. When the mature spores are discharged and reach a suitable substrate, they germinate and produce a small, flat, green, heart-shaped structure known as the prothallium or gametophytic (gamete-producing) generation. The gametophyte produces the sex organs antheridia (male) and archegonia (female). The gametes (sperm and egg) unite in fertilization and the resultant cell, or zygote, develops into the spore-bearing (sporophytic) fern plant.

In all ferns, the spores are produced in special multicellular organs known as sporangia. Except for a few genera, the sporangia are arranged in groups or clusters called sori. These are on the lower surface of the leaves or fertile fronds, either along the midrib of the pinnae, near the leaf margins, or scattered. Usually each sorus is covered by a flaplike structure called the indusium, which may be of various shapes and sizes. However, a few ferns have naked sori, and others have a false indusium formed by the folding or inrolling of the leaf margin. See also Polypodiophyta; Psilotophyta.

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Polypodiales
Polypodium californicum
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Polypodiopsida / Pteridopsida (disputed)
Order:	Polypodiales Link 1833
Families
See text.

The order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including tropical, semitropical and temperate areas. The characteristics of this group include: sporangia with a vertical annulus interrupted by the stalk and stomium; indusia laterally or centrally attached (or lost); gametophytes green, chordate, and surficial.^[1]

Polypodiales may be regarded as one of the most evolutionarily 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 the angiosperms. ^[2]

Contents 1 Families 2 Phylogenic relationships 3 Obsolete families 4 References 5 Sources

Families

The Polypodiales order includes the following families.^[3][4][5] The order in which they are listed is based on the order in which they appear in the phylogram that follows the list.

• Saccolomataceae Doweld & Reveal 2008
• Lonchitidaceae C.Presl ex M.R.Schomb. 1848
• Cystodiaceae J.R.Croft 1986
• Lindsaeaceae C.Presl ex M.R.Schomb. 1848
• Pteridaceae E.D.M.Kirchn. 1831
  • subfamily Cryptogrammoideae S.Linds. 2009 (=) Cryptogrammaceae Pic. Serm. 1963
  • subfamily Ceratopteridoideae (J.Sm.) R.M.Tryon 1986 (=) Ceratopteridaceae Underw. 1900
  • subfamily Pteridoideae C.Chr. ex Crabbe, Jermy & Mickel 1975
  • subfamily Cheilanthoideae W.C.Shieh 1973 (=) Cheilanthaceae B.K.Nayar 1970
  • subfamily Vittarioideae (C.Presl) Crabbe, Jermy & Mickel 1975 (=) Adiantoideae (C.Presl) R.M.Tryon 1986
• Dennstaedtiaceae Lotsy 1909

Eupolypods II

• Cystopteridaceae Schmakov 2001
• Rhachidosoraceae X.C.Zhang 2011
• Diplaziopsidaceae X.C.Zhang & Christenh. 2011
• Aspleniaceae Newman 1840
• Hemidictyaceae Christenh. 2011^[3][5]
• Thelypteridaceae Pic.Serm. 1970
• Woodsiaceae Herter 1949
• Onocleaceae Pic.Serm. 1970
• Blechnaceae Newman 1844
• Athyriaceae Alston 1956

Eupolypods I

• Hypodematiaceae Ching 1975
• Dryopteridaceae Herter 1949
  • subfamily Dryopteridoideae B.K.Nayar 1970
  • subfamily Elaphoglossoideae (Pic.Serm.) Crabbe, Jermy & Mickel 1975 (=) Elaphoglossaceae Pic.Serm.
• Lomariopsidaceae Alston 1956
• Nephrolepidaceae Pic.Serm. 1975
• Tectariaceae Panigrahi 1986
• Oleandraceae Ching ex Pic.Serm. 1965 (=) Olandraceae
• Davalliaceae M.R.Schomb. 1848
• Polypodiaceae J.Presl & C.Presl 1822
  • subfamily Loxogrammoideae H.Schneid. 2011
  • subfamily Drynarioideae Crabbe, Jermy & Mickel 1975
  • subfamily Platycerioideae B.K.Nayar 1970
  • subfamily Microsoroideae B.K.Nayar 1970
  • subfamily Polypodioideae B.K.Nayar 1970

Phylogenic relationships

The following diagram showing a likely phylogenic relationship between the families of the Polypodiales is based on Lehtonen, 2011,^[3] and Rothfels & al., 2012.^[6]

Polypodiales	Saccolomataceae Cystodiaceae Lonchitidaceae Lindsaeaceae Pteridaceae Dennstaedtiaceae eupolypods II Cystopteridaceae Rhachidosoraceae Diplaziopsidaceae Aspleniaceae Hemidictyaceae Thelypteridaceae Woodsiaceae Onocleaceae Blechnaceae Athyriaceae eupolypods I Hypodematiaceae Dryopteridaceae Lomariopsidaceae Nephrolepidaceae Tectariaceae Oleandraceae Davalliaceae Polypodiaceae

Obsolete families

Now-obsolete families of Polypodiales include:

• Drynariaceae - now in Polypodiaceae
• Grammitidaceae - now in Polypodiaceae
• Gymnogrammitidaceae - now in Polypodiaceae
• Loxogrammaceae - now in Polypodiaceae
• Nephrolepidaceae - now in Lomariopsidaceae
• Platyceriaceae - now in Polypodiaceae
• Pleursoriopsidaceae - now in Polypodiaceae
• Vittariaceae - now in Pteridaceae

References

1. ^ Alan R. Smith, Kathleen M. Pryer, Eric Schuettpelz, Petra Korall, Harald Schneider & Paul G. Wolf (2006). "A classification for extant ferns". Taxon 55 (3): 705–731. http://www.pryerlab.net/publication/fichier749.pdf. 
2. ^ Harald Schneider, Eric Schuettpelz, Kathleen M. Pryer, Raymond Cranfill, Susana Magallón, Richard Lupia (2004), "Ferns diversified in the shadow of angiosperms", Nature 428 (6982): 553–557, doi:10.1038/nature02361, PMID 15058303 
3. ^ ^{a b c} Samuli Lehtonen (2011). "Towards Resolving the Complete Fern Tree of Life". PLoS ONE 6 (10): e24851. http://www.sci.utu.fi/sivustot/amazon/publications/articles/pdf_pub/Lehtonen_2011_PLoS1.pdf. 
4. ^ Maarten J. M. Christenhusz, Xian-Chun Zhang & Harald Schneider (2011). "A linear sequence of extant families and genera of lycophytes and ferns". Phytotaxa 19: 7–54. http://www.mapress.com/phytotaxa/content/2011/f/pt00019p054.pdf. 
5. ^ ^{a b} Maarten J. M. Christenhusz & Harald Schneider (2011). "Corrections to Phytotaxa 19: Linear sequence of lycophytes and ferns". Phytotaxa 28: 50–52. http://www.mapress.com/phytotaxa/content/2011/f/pt00028p052.pdf. 
6. ^ Carl J. Rothfels, Anders Larsson, Li-Yaung Kuo, Petra Korall, Wen- Liang Chiou, Kathleen M. Pryer (2012). "Overcoming Deep Roots, Fast Rates, and Short Internodes to Resolve the Ancient Rapid Radiation of Eupolypod II Ferns". Systematic Biology 61 (1): 70. http://sysbio.oxfordjournals.org/content/early/2012/01/04/sysbio.sys001.short?rss=1. 

Sources

• Eric Schuettpelz. THE EVOLUTION AND DIVERSIFICATION OF EPIPHYTIC FERNS. PhD Thesis Duke University 2007
• Michael Hassler and Brian Swale. Checklist of Ferns and Fern Allies 2001
• Australian National Botanic Gardens. A classification of the ferns and their allies

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