A plant in the wrong place, being one that occurs opportunistically on land or in water that has been disturbed by human activity (see ruderal) or on cultivated land, where it competes for nutrients, water, sunlight, or other resources with cultivated plants. Under different circumstances the plant may itself be cultivated (e.g. it may grow from seed or propagate vegetatively from the residue of a previous crop). The presence of weeds among crop plants can result in reduced yield because of competition; in gardens weeds may be unsightly; in waterways they can become a hindrance to navigation (e.g. the water hyacinth, Eichhornia crassipes).
Subjects: Ecology and Conservation.