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| Pterophyta, the Ferns | ||||
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 Tree fern | ||||
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Fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pterophyta or Filicophyta. A fern is defined as a vascular plant that reproduces by shedding spores to initiate an alternation of generations. New fronds arise by circinate vernation (leaf formation by unrolling).
| Table of contents |
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2 Fern structure 3 Classification 4 Economic Uses 5 External Links |
The life cycle of a typical fern consists of two distinct stages or generation phases (see alternation of generations), proceeding as follows:
A sporophytic fern consists of:
Ferns have traditionally been grouped in the class Filices, but some modern classifications assign them their own division in the plant kingdom, which may be known as Pterophyta or Filicophyta. This may be subdivided into four main groups, or classes (or orders if the ferns are considered as a class):
Fern life cycle
Fern structure
Classification
The last group includes most plants familiarly known as ferns. A group of plants termed ophioglossoids was once considered among the true ferns, but is now regarded as an isolated group (see "fern-allies." These are species formerly grouped in the Family Ophioglossaceae: adders-tongues and grape-ferns.
A more complete classification scheme follows:
Ferns are not as economically important as, say, cereal grains, with one possible exception. Ferns of the genus Azolla, which are very small, floating plants which do not look like ferns, and are called mosquito fern, are used as a biological fertilizer in the rice paddies of southeast Asia.
Other ferns with economic significance include:
External Links