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{{ otheruses1|plants specifically called weeds}} {{ otheruses1|plants specifically called weeds}}
], a ] native to southern Europe and the Middle East that is an invasive weed in parts of ].]] ], a ] native to southern Europe and the Middle East that is an invasive weed in parts of ].]]
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A '''weed''' in a general sense is a ] that is considered by the user of the term to be a ], and normally applied to unwanted plants in human-made settings such as ]s, ]s or ] areas, but also in parks, woods and other natural areas. More specifically, the term is often used to describe ] or nonnative plants that grow and reproduce aggressively.<ref>ISBN 0-7167-1031-5 Janick, Jules. ''Horticultural Science.'' San Francisco: W.H. Freeman, 1979. Page 308.</ref> A '''weed''' in a general sense is a ] that is considered by the user of the term to be a ], and normally applied to unwanted plants in human-made settings such as ]s, ]s or ] areas, but also in parks, woods and other natural areas. More specifically, the term is often used to describe ] or nonnative plants that grow and reproduce aggressively.<ref>ISBN 0-7167-1031-5 Janick, Jules. ''Horticultural Science.'' San Francisco: W.H. Freeman, 1979. Page 308.</ref>


Weeds may be unwanted because they are unsightly, or they limit the growth of other plants by blocking light or using up ]s from the ]. They also can harbor and spread plant ]s that can infect and degrade the quality of ] or ] plants. Weeds may be a nuisance because they have thorns or prickles, cause skin irritation when contacted, or parts of the plants might come off and attach to fur or clothes. '''Robin Foster Is A WEED!!!'''Weeds may be unwanted because they are unsightly, or they limit the growth of other plants by blocking light or using up ]s from the ]. They also can harbor and spread plant ]s that can infect and degrade the quality of ] or ] plants. Weeds may be a nuisance because they have thorns or prickles, cause skin irritation when contacted, or parts of the plants might come off and attach to fur or clothes.


==Definition== ==Definition==

Revision as of 23:50, 14 March 2008

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For other uses, see plants specifically called weeds.
Yellow starthistle, a thistle native to southern Europe and the Middle East that is an invasive weed in parts of North America.

A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-made settings such as gardens, lawns or agricultural areas, but also in parks, woods and other natural areas. More specifically, the term is often used to describe native or nonnative plants that grow and reproduce aggressively.

Robin Foster Is A WEED!!!Weeds may be unwanted because they are unsightly, or they limit the growth of other plants by blocking light or using up nutrients from the soil. They also can harbor and spread plant pathogens that can infect and degrade the quality of crop or horticultural plants. Weeds may be a nuisance because they have thorns or prickles, cause skin irritation when contacted, or parts of the plants might come off and attach to fur or clothes.

Definition

The term weed in its general sense is a subjective one, without any classification value, since a weed is not a weed when growing where it belongs or is wanted. Indeed, a number of "weeds" have been used in gardens or other cultivated-plant settings. An example is the corncockle, Agrostemma, which was a common field weed exported from Europe along with wheat, but now sometimes grown as a garden plant.

Distribution

Weedy plants generally share similar adaptations that give them advantages and allow them to proliferate in disturbed environments whose soil or natural vegetative cover has been damaged. Naturally occurring disturbed environments include dunes and other windswept areas with shifting soils, alluvial flood plains, river banks and deltas, and areas that are often burned. Since human agricultural practices often mimic these natural environments where weedy species have evolved, weeds have adapted to grow and proliferate in human-disturbed areas such as agricultural fields, lawns, roadsides, and construction sites.

The weedy nature of these species often gives them an advantage over more desirable crop species because they often grow quickly and reproduce quickly, have seeds that persist in the soil seed bank for many years, or have short lifespans with multiple generations in the same growing season. Perennial weeds often have underground stems that spread out under the soil surface or, like ground ivy (Glechoma hederacea), have creeping stems that root and spread out over the ground. A number of weedy species have developed allelopathy, chemical means to prevent the germination or growth of neighboring plants.

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Weeds and people

As long as people have cultivated plants, weeds have been a problem. Weeds have even found their way into religious and literature texts as these quotes from Genesis and a Shakespearean Sonnet show:

"Cursed is the ground because of you; through painful toil you will eat of it all the days of your life. It will produce thorns and thistles for you, and you will eat the plants of the field. By the sweat of your brow you will eat your food until you return to the ground,"

"To thy fair flower add the rank smell of weeds: But why thy odour matcheth not thy show, The soil is this, that thou dost common grow."

Weeds and human civilization have a long history. Often weedy plant seeds are collected and transported with crops after the harvesting of grains, so that many of these weed species have moved out of their natural geographic locations and have spread around the world with humans. (See Invasive species.) Not all weeds have the same ability to damage crops and horticultural plants. Some have been classified as noxious weeds because if left unchecked, they often dominate the environment where crop plants are to be grown. They are often foreign species mistakenly or accidentally imported into a region where there are few natural controls to limit their spread and population. With the conversion of land to agriculture producing large areas of open soil and human distribution of food crops mixed with seeds of weeds from other parts of the world, many weeds have ideal areas for growth and reproduction. With Humans being the vector of transport and producer of disturbed environments, weedy species have an ideal association with humans and our impact on the globel environment.

A number of weeds, such as the dandelion Taraxacum, are edible, and their leaves and roots may be used for food or herbal medicine. Burdock is common weed over much of the world, and is sometimes used to make soup and other medicine in East Asia. These so-called "beneficial weeds" may have other beneficial effects, such as drawing away the attacks of crop-destroying insects but often are breeding grounds for insects and pathogens that attack other plants. Dandelions besides being a weed in lawns, are one of several species which break up hardpan in overly cultivated fields, helping crops grow deeper root systems. Some modern species of domesticated flower actually originated as weeds in cultivated fields and have been breed by people into garden plants for their flowers or foliage.

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See also

References

  1. ISBN 0-7167-1031-5 Janick, Jules. Horticultural Science. San Francisco: W.H. Freeman, 1979. Page 308.
  2. http://davesgarden.com/pf/go/1341/
  3. http://employees.csbsju.edu/ssaupe/biol327/Lecture/foraging_case_study.htm
  4. Genesis 3:17-19 New International Version
  5. http://www.infoplease.com/t/lit/shakespeare-sonnets/69.html



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