Polypodiophyta - Reference Center

Columbia Encyclopedia entry: Polypodiophyta

Polypodiophytapŏl′ēpō′dēŏf'ətə, division of the plant kingdom consisting of the plants commonly called ferns. The ferns are vascular plants with stems, roots, and leaves. The small and inconspicuous gametophyte and the large spore-producing fern plant are quite independent of each other. The sporophyte plant, which is the plant form popularly recognized as a fern, may have an erect stem of more than 50 ft (16 m) in height, or a prostrate stem lying in or on the ground. The anatomy of fern stems, especially in the arrangement of the vascular bundles, differs greatly from group to group and is used as a means of interpreting the evolutionary relationships of the various groups. Typically, the leaf, or frond, is large and much divided, although many ferns have simple leaves, i.e., leaves with the blade undivided. Fern leaves generally unroll as they develop from a coiled early bud stage called the fiddlehead or crozier. Sporangia, the spore-producing structures, are generally found on the back of the leaf, but occasionally occur on special structures, which are probably evolutionarily modified leaves. In the great majority of ferns, the spore cases, or sporangia, are produced in groups, with each group called a sorus. These sori can often be seen on the back of the leaves. The sporangia in the sorus are usually protected in some manner, sometimes by an umbrellalike structure, the indusium, and sometimes by the inrolling of the leaf edge. The sporangium consists of a jacket of thin cells, partly surrounded at one side by a row of very thick-walled cells, the annulus. When the spores are mature, a springlike mechanism in the annulus serves to tear open the sporangium and eject the spores. Germinating spores produce a green, thin, sometimes heart-shaped, gametophyte, or prothallus, on the lower side of which are produced the sex organs, the sperm-producing antheridia and the egg-producing archegonia. The gametophytes are thin and delicate and thrive only in moist places; the lower side usually has a film of water, which facilitates the swimming of the motile, flagellated sperm from an antheridium to the neck of an archegonium and to the egg within it. The resulting diploid zygote develops slowly into a mature sporophyte with stem, root, and leaves. Ferns were abundant in Carboniferous times, and many are known only from fossil records. Of the 10,000 known species of living ferns, almost all belong to the order Filicales (true ferns). The grape ferns and the adder's-tongue ferns, of the order Ophioglossales, are very few in number. The genus Marsilea, of the order Marsileales, and the genera Salvinia and Azolla, both of the order Salviniales, have complex life histories. Marsilea grows in wet places, and Salvinia and Azolla float on the surfaces of ponds and lakes.

Wikipedia search results for: Fern

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A fern (redirected from Polypodiophyta) is any one of a group of about 12,000 species of plants. Chapman, Arthur D.. Numbers of Living Species in Australia and the World. Report for the Australian Biological Resources Study. Canberra, Australia. September 2009. http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/index.html Unlike mosses, they have xylem and phloem. They have stems, leaves, and roots like other vascular plants. Ferns do not have either seeds or flowers. By far the largest group of ferns are the leptosporangiate ferns, but ferns as defined here include horsetails, whisk ferns, marattioid ferns, and ophioglossoid ferns. The term...more »

Columbia Encyclopedia search results: Polypodiophyta

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sweet fern
Sweet fern, common name for several plants belonging to different botanical divisions. One is a shrub of the family Myricaceae (bayberry family) in the division Magnoliophyta; others are plant...
fern
Fern, any plant of the division Polypodiophyta. Fern species, numbering several thousand, are found throughout the world but are especially abundant in tropical rain forests. The ferns and the...
bracken
Bracken or brake, common name for a tall fern (Pteridium aquilinum) with large triangular fronds, widespread throughout the world, often as a weed. It is considered poisonous to livestock when...
plant
Plant, any organism of the plant kingdom, as opposed to one of the animal kingdom or of the kingdoms Fungi, Protista, or Monera in the five-kingdom system of classification. (A more recent sys...

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