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This article is about plants specifically called weeds. For other uses, see Weed (disambiguation). See also: Invasive species
A dandelion is a common weed all over the world, especially in Europe, Asia and the Americas.

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. Generally, a weed is a plant in an undesired place.

Weeds may be unwanted for a number of reasons: they might be unsightly, or crowd out or restrict light to more desirable plants or use limited nutrients from the soil. They can harbor and spread plant pathogens that infect and degrade the quality of crop or horticultural plants. Some weeds are a nuisance because they have thorns or prickles, some have chemicals that cause skin irritation or are hazardous if eaten, or have parts that come off and attach to fur or clothes.

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.

Professor Richard C. Lewontin of Harvard University defines weeds as plants that create environmental conditions in which it cannot reproduce. He takes the example of pine trees that crowd out sunlight such that its own offspring cannot grow. Weeds continue to exist, because the environment is continually being disturbed to create open conditions for new generations, such as forest fires and human activity.

Weed is bad.

Weed is bad

Examples

The five plants designated "injurious weeds" under UK law are:

See also

References

  1. Janick, Jules (1979). Horticultural Science (3rd ed.). San Francisco: W.H. Freeman. p. 308. ISBN 0-7167-1031-5.
  2. "Detailed information on Corn Cockle (Agrostemma githago)". PlantFiles. Retrieved February 15, 2009.
  3. A speech given on the radio program Big Ideas, (5/11/2003): "A weed is literally a plant... which comes into a disturbed habitat, which then changes the nature of the soil, the shading, and everything, and the moisture, ectcetera, in such a way that it cannot reproduce itself in that habitat."
  4. On lawns and elsewhere, some people consider clover a weed, and some do not, as it has some beneficial effects.
  5. "PLANTS Profile for Cannabis sativa (marijuana)". Natural Resources Conservation Service. United States Department of Agriculture. Retrieved February 15, 2009.
  6. Mathre, Mary Lynn, ed. (1997). Cannabis in medical practice: a legal, historical and pharmacological overview of the therapeutic use of Marijuana. Jefferson, NC: McFarland. p. 208. ISBN 9780786403615. Retrieved February 15, 2009.
  7. "Weeds Act 1959". Department for Environment, Food and Rural Affairs (Defra), UK. Archived from the original on 2007-09-26. Retrieved February 15, 2009. {{cite web}}: Text "DEFRA UK," ignored (help)

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