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Fern

2007 Schools Wikipedia Selection. Related subjects: Plants

                  iFerns (Pteridophyta)
   Polystichum setiferum showing unrolling young frond
   Polystichum setiferum showing unrolling young frond
                Scientific classification

   Kingdom:  Plantae
   Division: Pteridophyta

                                   Classes

   Marattiopsida
   Osmundopsida
   Gleicheniopsida
   Pteridopsida

   A fern is any one of a group of about 20,000 species of plants
   classified in the phylum or division Pteridophyta, also known as
   Filicophyta. The group is also referred to as polypodiophyta, or
   polypodiopsida when treated as a subdivision of tracheophyta (vascular
   plants). The study of ferns is called pteridology; one who studies
   ferns is called a pteridologist. The term pteridophytes has
   traditionally been used to describe all seedless vascular plants so is
   synonymous with "ferns and fern allies". This can be confusing given
   that the fern phylum Pteridophyta is also sometimes referred to as
   pteridophytes.

   A fern is a vascular plant that differs from the more primitive
   lycophytes in having true leaves (megaphylls), and from the more
   advanced seed plants ( gymnosperms and angiosperms) in lacking seeds.
   Like all vascular plants, it has a life cycle, often referred to as
   alternation of generations, characterised by a diploid sporophytic and
   a haploid gametophytic phase. Unlike the gymnosperms and angiosperms,
   in ferns the gametophyte is a free-living organism. The life cycle of a
   typical fern is as follows:
    1. A sporophyte ( diploid) phase produces haploid spores by meiosis;
    2. A spore grows by cell division into a gametophyte, which typically
       consists of a photosynthetic prothallus
    3. The gametophyte produces gametes (often both sperm and eggs on the
       same prothallus) by mitosis
    4. A mobile, flagellate sperm fertilizes an egg that remains attached
       to the prothallus
    5. The fertilized egg is now a diploid zygote and grows by mitosis
       into a sporophyte (the typical "fern" plant).

Fern structure

   Ferns at the Royal Melbourne Botanical Gardens
   Enlarge
   Ferns at the Royal Melbourne Botanical Gardens
   Tree ferns, probably Dicksonia antarctica
   Enlarge
   Tree ferns, probably Dicksonia antarctica

   Like the sporophytes of seed plants, those of ferns consist of:
     * Stems: Most often an underground creeping rhizome, but sometimes an
       above-ground creeping stolon (e.g., Polypodiaceae), or an
       above-ground erect semi-woody trunk (e.g., Cyatheaceae) reaching up
       to 20 m in a few species (e.g., Cyathea brownii on Norfolk Island
       and Cyathea medullaris in New Zealand).
     * Leaf: The green, photosynthetic part of the plant. In ferns, it is
       often referred to as a frond, but this is because of the historical
       division between people who study ferns and people who study seed
       plants, rather than because of differences in structure. New leaves
       typically expand by the unrolling of a tight spiral called a
       crozier or fiddlehead. This uncurling of the leaf is termed
       circinate vernation. Leaves are divided into two types:
          + Trophophyll: A leaf that does not produce spores, instead only
            producing sugars by photosynthesis. Analogous to the typical
            green leaves of seed plants.
          + Sporophyll: A leaf that produces spores. These leaves are
            analogous to the scales of pine cones or to stamens and pistil
            in gymnosperms and angiosperms, respectively. Unlike the seed
            plants, however, the sporophylls of ferns are typically not
            very specialized, looking similar to trophophylls and
            producing sugars by photosynthesis as the trophophylls do.
     * Roots: The underground non-photosynthetic structures that take up
       water and nutrients from soil. They are always fibrous and are
       structurally very similar to the roots of seed plants.

   The gametophytes of ferns, however, are very different from those of
   seed plants. They typically consist of:
     * Prothallus: A green, photosynthetic structure that is one cell
       thick, usually heart- or kidney-shaped, 3-10 mm long and 2-8 mm
       broad. The thallus produces gametes by means of:
          + Antheridia: Small spherical structures that produce flagellate
            sperm.
          + Archegonia: A flask-shaped structure that produces a single
            egg at the bottom, reached by the sperm by swimming down the
            neck.
     * Rhizoids: root-like structures (not true roots) that consist of
       single greatly-elongated cells, water and mineral salts are
       absorbed over the whole structure. Rhizoids anchor the prothallus
       to the soil.

Evolution and classification

   Ferns first appear in the fossil record in the early-Carboniferous
   period. By the Triassic, the first evidence of ferns related to several
   modern families appeared. The "great fern radiation" occurred in the
   late-Cretaceous, when many modern families of ferns first appeared.

   Ferns have traditionally been grouped in the Class Filices, but modern
   classifications assign them their own division in the plant kingdom,
   called Pteridophyta.

   Traditionally, three discrete groups of plants have been considered
   ferns: the adders-tongues, moonworts, and grape-ferns (
   Ophioglossophyta), the Marattiaceae, and the leptosporangiate ferns.
   The Marattiaceae are a primitive group of tropical ferns with a large,
   fleshy rhizome, and are now thought to be a sibling taxon to the main
   group of ferns, the leptosporangiate ferns. Several other groups of
   plants were considered " fern allies": the clubmosses, spikemosses, and
   quillworts in the Lycopodiophyta, the whisk ferns in Psilotaceae, and
   the horsetails in the Equisetaceae. More recent genetic studies have
   shown that the Lycopodiophyta are only distantly related to any other
   vascular plants, having radiated evolutionarily at the base of the
   vascular plant clade, while both the whisk ferns and horsetails are as
   much true ferns as are the Ophioglossoids and Marattiaceae. In fact,
   the whisk ferns and Ophioglossoids are demonstrably a clade, and the
   horsetails and Marattiaceae are arguably another clade.

   One possible means of treating this situation is to consider only the
   leptosporangiate ferns as "true" ferns, while considering the other
   three groups as "fern allies".

   The true ferns may be subdivided into six main groups, or classes (or,
   if the true ferns are considered as a class, then the last three would
   be orders):
     * Ophioglossopsida
     * Equisetopsida
     * Marattiopsida
     * Osmundopsida
     * Gleicheniopsida
     * Pteridopsida

   The last group includes most plants familiarly known as ferns. Modern
   research indicates that the Osmundopsida diverged first from the common
   ancestor of the leptosporangiate ferns, followed by the Gleichenopsida.

   A more complete classification scheme follows:
     * Division: Pteridophyta
          + Class: Ophioglossopsida
               o Order: Ophioglossales
               o Order: Psilotales
          + Class: Equisetopsida
               o Order: Equisetales
          + Class: Marattiopsida
               o Order: Marattiales
               o Order: Christenseniales
          + Class: Osmundopsida
               o Order: Osmundales (the flowering ferns)
          + Class: Gleicheniopsida
               o Subclass: Gleicheniatae
                    # Order: Gleicheniales (the forked ferns)
                    # Order: Dipteridales
                    # Order: Matoniales
               o Subclass: Hymenophyllatae
                    # Order: Hymenophyllales (the filmy ferns)
               o Subclass: Hymenophyllopsitae
                    # Order: Hymenophyllopsidales
          + Class: Pteridopsida
               o Subclass: Schizaeatae
                    # Order: Schizeales (including the climbing ferns)
               o [heterosporous ferns]
                    # Order: Marsileales (Hydropteridales) (the
                      water-clovers, mosquito fern, water-spangle)
               o Subclass: Cyatheatae
                    # Order: Cyatheales (the tree ferns)
                    # Order: Plagiogyriales
                    # Order: Loxomales
               o Subclass: Pteriditae
                    # Order: Lindseales
                    # Order: Pteridales (including the brakes and
                      maidenhair ferns)
                    # Order: Dennstaedtiales (the cup ferns, including
                      bracken)
               o Subclass: Polypoditae
                    # Order: Aspleniales (the spleenworts)
                    # Order: Athyriales (including the lady ferns, ostrich
                      fern, maiden ferns, etc.)
                    # Order: Dryopteridales (the wood ferns and sword
                      ferns)
                    # Order: Davalliales (including the rabbits-foot ferns
                      and Boston ferns)
                    # Order: Polypodiales (including the rock-cap ferns or
                      Polypodies)

Economic uses

   Ferns are not as important economically as seed plants but have
   considerable importance. Ferns of the genus Azolla are very small,
   floating plants that do not look like ferns. Called mosquito fern, they
   are used as a biological fertilizer in the rice paddies of southeast
   Asia, taking advantage of their ability to fix nitrogen from the air
   into compounds that can then be used by other plants. A great many
   ferns are grown in horticulture as landscape plants, for cut foliage
   and as houseplants, especially the Boston fern (Nephrolepis exaltata).
   Several ferns are noxious weeds or invasive species, including Japanese
   climbing fern ( Lygodium japonicum), mosquito fern and sensitive fern
   (Onoclea sensibilis). Giant water fern ( Salvinia molesta) is one of
   the world's worst aquatic weeds. The important fossil fuel coal
   consists of the remains of primitive plants, including ferns.

   Other ferns with some economic significance include:
     * Dryopteris filix-mas (male fern), used as a vermifuge
     * Rumohra adiantoides (floral fern), extensively used in the florist
       trade
     * Osmunda regalis (royal fern) and Osmunda cinnamomea (cinnamon
       fern), the root fibre being used horticulturally; the fiddleheads
       of O. cinnamomea are also used as a cooked vegetable
     * Matteuccia struthiopteris (ostrich fern), the fiddleheads used as a
       cooked vegetable in North America
     * Pteridium aquilinum (bracken), the fiddleheads used as a cooked
       vegetable in Japan and are believed to be responsible for the high
       rate of stomach cancer in Japan
     * Diplazium esculentum (vegetable fern), a source of food for some
       native societies
     * Pteris vittata (brake fern), used to absorb arsenic from the soil
     * Polypodium glycyrrhiza (licorice fern), roots chewed for their
       pleasant flavor
     * Tree ferns, used as building material in some tropical areas
     * Bracken fern, often poisons cattle and horses
     * Cyathea cooperi (Australian tree fern), an important invasive
       species in Hawaii
     * Dryopteris filix-mas, this fern accidentally sprouting in a bottle
       resulted in Nathaniel Bagshaw Ward's 1829 invention of the
       terrarium or Wardian case
     * Ceratopteris richardii, a model plant for teaching and research,
       often called C-fern

Cultural connotations

   In Slavic folklore, ferns are believed to bloom once a year, during the
   Ivan Kupala night. Although it's exceedingly difficult to find, anyone
   who takes a look of a fern-flower will be happy and rich for the rest
   of his life. Similarly in Finland, the tradition holds that one who
   finds the seed of a fern in bloom on Midsummer night, will by the
   posession of it be able to travel under a glamour of invisibility and
   shall be guided to the locations where eternally blazing Will o' the
   wisps mark the spot of hidden treasure caches.

Misunderstood names

   Several non-fern plants are called "ferns" and are sometimes popularly
   believed to be ferns in error. These include:
     * "Asparagus fern" - This may apply to one of several species of the
       monocot genus Asparagus, which are flowering plants. A better name
       would be "fern asparagus".
     * "Sweetfern" - This is a shrub of the genus Comptonia.
     * " Air fern" - This is an unrelated aquatic animal that is related
       to a coral; it is harvested, dried, dyed green, then sold as plant
       that can "live on air". It looks like a fern but is actually a
       skeleton.

   In addition, the book Where the Red Fern Grows has elicited many
   questions about the mythical "red fern" named in the book. There is no
   such known plant, although there has been speculation that the Oblique
   grape-fern, Sceptridium dissectum, could be referred to here, because
   it is known to appear on disturbed sites and its fronds may redden over
   the winter.

Gallery

   Fern leaf, probably Blechnum nudum

   A tree fern unrolling a new frond

   Tree fern, probably Dicksonia antarctica

   Tree ferns, probably Dicksonia antarctica

   "Filicinae" from Ernst Haeckel's Kunstformen der Natur, 1904

   Unidentified tree fern in Oaxaca

   Tree Fern Spores San Diego, CA

   Leaf of fern

   Unidentified fern with spores showing in Rotorua, NZ.

   Retrieved from " http://en.wikipedia.org/wiki/Fern"
   This reference article is mainly selected from the English Wikipedia
   with only minor checks and changes (see www.wikipedia.org for details
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