Polypodiales

(botany) The true ferns; the largest order of modern ferns, distinguished by being leptosporangiate and by having small sporangia with a definite number of spores.

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.

The noun has one meaning:

Meaning #1: true (leptosporangiate) ferns
  Synonyms: Filicales, order Filicales, order Polypodiales

Polypodiales
Polypodium californicum
Scientific classification
Kingdom:	Plantae
Division:	Pteridophyta
Class:	Polypodiopsida
Order:	Polypodiales
Families
Aspleniaceae Blechnaceae Davalliaceae Dennstaedtiaceae Dryopteridaceae Lindsaeaceae Lomariopsidaceae Oleandraceae Onocleaceae Polypodiaceae Pteridaceae Saccolomataceae Tectariaceae Thelypteridaceae Woodsiaceae

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]

The 15 families of Polypodiales are listed here from those considered most basal to those considered most derived^[3]:

• Lindsaeaceae
• Saccolomataceae
• Dennstaedtiaceae
• Pteridaceae
• Aspleniaceae
• Thelypteridaceae
• Woodsiaceae
• Blechnaceae
• Onocleaceae
• Dryopteridaceae
• Lomariopsidaceae
• Tectariaceae
• Oleandraceae (formerly Olandraceae)
• Davalliaceae
• Polypodiaceae

Now-obsolete families of Polypodiales:

• 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

References

• Checklist of Ferns and Fern Allies

1. ^ Smith, A. R., K. M. Pryer, et al. (2006). "A classification for extant ferns." Taxon 55(3): 705-731
2. ^ "Ferns diversified in the shadow of angiosperms", Nature 428 (6982): 553–557, 2004, doi:10.1038/nature02361, PMID 15058303 
3. ^ Smith, A. R., K. M. Pryer, et al. (2006). "A classification for extant ferns." Taxon 55(3): 705-731

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