Fern
| Pteridophyta, the Ferns | ||||
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Tree fern | ||||
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| Classes | ||||
Fern, or pteridophyte, is any one of a group of some twenty thousand species of plants classified in the Division Pteridophyta, formerly known by some as Filicophyta. A fern is defined as a vascular plant that lacks seeds, and 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 Evolution and Classification 4 Economic uses 5 Misunderstood names 6 External links and references |
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 first appear in the fossil record in the early Carboniferous epoch. By the Triassic the first evidence of ferns related to several modern families appears. The great fern radiation occurred in the late Cretaceous, where many modern families of ferns first appear.
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 Pteridophyta.
Two related groups of plants, commonly known as ferns, are more distantly related to the main group of ferns: the whisk ferns (Psilophyta) and the adders-tongues, moonworts and grape-ferns (Ophioglossophyta). The Ophioglossophytes were formerly considered "true" ferns, and were grouped in the family Ophioglossaceae, but were subsequently found to be more distantly related. Some classification systems include the Psilopytes and Ophioglossophytes in division Pteridophyta, while others assign them separate divisions. Modern phylogeny indicates that the Ophioglossophytes, Psilopytes, and true ferns together constitute a monophyletic group, descended from a common ancestor.
The "true" ferns may be subdivided into four main groups, or classes (or orders if the ferns are considered as a class):
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:
Fern life cycle
Fern structure
Evolution and Classification
Economic uses
In addition, a great many ferns are grown horticulturally. The leatherleaf fern or fancy fern, Rumohra adiantoides, is an especial favorite among florists who use its cut fronds in flower arrangements.Misunderstood names
Several non-fern plants are called "ferns" and are sometimes popularly believed to be ferns in error. These include:
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.External links and references