Real ferns

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Real ferns
Common fern (Dryopteris filix-mas)

Common fern ( Dryopteris filix-mas )

Systematics
without rank: Phragmoplastophyta
without rank: Streptophyta
Empire : Plants (Plantae)
Department : Vascular plants (tracheophyta)
Ferns
Class : Real ferns
Scientific name
Polypodiopsida
Cronquist , Takht. & Zimmerm.

The real ferns (Polypodiopsida, Syn .: Filicopsida, Pteridopsida) are a class within the ferns . It includes the leptosporangiate ferns , while the ferns formerly known as eusporangiat are now placed in the classes Marratiopsida and Psilotopsida .

The class includes around 11,000 species.

features

The characteristics of the ferns also apply to the real ferns.

The sporangia of the real fern develop from a single cell. The wall of the mature sporangium consists of only one layer of cells (leptosporangiat). Most sporangia open with a special annulus that helps disperse the spores . Usually 64 spores are formed per sporangium.

Most of the ferns are herbaceous and have a rhizome . In the case of Pteridium, this can live to be 70 years and reach 40 meters in length. There are also tree-shaped ferns with trunks as thick as arms in the tropics. The tribes have a central proto in youth stele , which merge at the age in the form of rich Siphono- and Polystelen. In the vascular bundles , the xylem is inside and the phloem is outside. They are surrounded by an endodermis . There is no secondary growth in thickness . The stability of the trunks comes from the leaf traces, from sclerenchymal plates and, in some tree ferns, from a thick coat of sprout roots.

The leaves are megaphylls, which are often pinnate and form the classic frond. The leaves grow with a double-edged apex cell and are often characteristically curled up during growth.

The sporangia are located in large numbers on the underside of the photosynthesizing leaves ( sporotrophophylls ). Usually the spore-bearing leaves do not differ from the sterile ones. The ostrich fern is an exception . The sporangia are usually united to form sori . The spores are mostly of the same size (isospore), the clover fern family and the swimming fern family are heterosporous.

The prothallia (the gametophyte ) are short-lived. With the exception of the heterospore ferns, they are hermaphroditic. Only in the Australian genus Platyzoma (Gleicheniaceae) are the prothallia dioecious. The antheridia and archegonia arise on the underside of the prothallia.

distribution

True ferns are widespread worldwide, especially on oceanic islands and in the middle altitudes of the tropics , where they have developed from forms only a few millimeters in size (e.g. didymoglossum , skin fern family ) to tree ferns (Cyatheaceae) 20 meters in size .

Systematics and evolution

The oldest known fossils of leptosporangiate ferns date from the early Carboniferous . There were at least six families at the end of the Carboniferous. In the Permian, Triassic and Jurassic, these were replaced by representatives of families that still exist today (Osmundaceae, Schizaeaceae, Matoniaceae, Dipteridaceae and others). The polypodiales , the largest order today with 80 percent of all species, only reached its diversity from the Cretaceous onwards , that is, in parallel with the angiosperms.

The real ferns are according to the system used here by Smith et al. (2006) subdivided as follows:

For the individual genera of the families, see the Fern Systematics .

Among the leptosporangiate ferns there are the following extinct families:

literature

Individual evidence

  1. ↑ Klaus Mehltreter, Lawrence R. Walker, Joanne M. Sharpe: Fern ecology . Cambridge University Press, Cambridge 2010, ISBN 978-0-521-72820-1 ( cambridge.org [accessed January 4, 2020]).
  2. ↑ Smith et al .: A classification for extant ferns 2006.
  3. ^ Thomas N. Taylor, Edith L. Taylor, Michael Krings: Paleobotany. The Biology and Evolution of Fossil Plants . 2nd Edition. Elsevier / Academic Press, Amsterdam et al. 2009, ISBN 978-0-12-373972-8 , pp. 386 ( limited preview in Google Book Search).

Web links

Commons : True Ferns ( Polypodiopsida )  - Collection of images, videos and audio files