Hello
Such plants are called "escapes"
Many cultivated plants escape from the confines of their cultivation,
and some are considered to be serious problems.
The American Heritage dictionary defines a weed as: "A plant
considered undesirable, unattractive, or troublesome, especially one
growing where it is not wanted"
By that definition, technically any "escape" could be considered to be
a weed, as long as it is growing where people don't want it to grow.
But some plants are more likely to become weeds than others and much
more likely to grow where they are not wanted. These traits that tend
to make an escaped plant thrive include (among others):
- long-lived seeds that don't all germinate at the same time
- rapid seedling growth
- high tolerance to changes in environment, and ability to grow in
different environments
- competes aggressively with other plants
- produces new seeds continuously
- produces a large number of seeds
- can disperse its seeds long distances
Although "escapes" don't always have all of these characteristics,
most that become a problem do have some combination of them.
"Escapes" have come into the news recently, with the introduction of
Genetic Engineering. Most crop plants have significant limitations in
their plant growth and seed dispersal habits which prevent them from
surviving long without constant care from humans, much less thriving
in the wild as weeds. Genetic engineering could conceivably improve a
plant's ability to "escape" into the wild, and this is causing great
debate in scientific circles.
The following terms are also sometimes used to describe "escapes" in
certain circumstances.
Exotic: a non-indigenous species, or one introduced, either
purposefully or accidentally.
Naturalized exotic: an exotic that has escaped into the wild where it
reproduces on its own either sexually or asexually and has done so
over a long period of time.
Invasive: a word sometimes used to describe "escapes" that are out of
control.
Scientists take escapes seriously, and generally rank them as to their
"destructiveness"
This is taken from the "Invasive Plant Pest Definitions" site at
( http://sain.nbii.gov/invasives/inv_plant_pest_def.shtml )
"A-ranked species exhibit the most invasive tendencies in natural
areas and native plant habitats. They may disrupt ecosystem processes
and cause major alterations in plant community composition and
structure. They establish readily in natural systems and spread
rapidly."
"B-ranked species exhibit moderate invasiveness in natural areas. They
may have minor influence on ecosystem processes, alter plant community
composition and affect community structure in at least one layer. They
may become dominant in the understory layer without threatening all
species found in the community. These species usually require a minor
disturbance to become established."
"C-ranked species generally do not affect ecosystem processes but may
alter plant community composition by out-competing one or more native
plant species. They often establish in severely disturbed areas. The
disturbance may be natural or human origin, such as ice-storm damage,
wind-throw, or road construction. These species spread slowly or not
at all from disturbed sites."
Hope that helps.
Willie-ga
A list of invasive escapes, compiled by the Connecticut Invasive Plant
Working Group
http://darwin.eeb.uconn.edu/ccb/publications/publication-1.html
Google Search Terms used
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