Characteristics, significance, and human dimension of global invasive weeds - Invasive Plants: Ecological and Agricultural Aspects - page 230

Table 4. Intentional introduction of some weeds to India 1

Scientific name Common name Introduced from Purpose

Chromolaena odorata Siam weed Tropical areas Cover crop

Eichnonia crassipes Water hyacinth South America Ornamental

Lantana camera Lantana Many countries Ornamental

Mikania micantha Miconia Malaysia Cover crop

Opuntia stricta Opuntia Australia Hedge plant

Phaseolus labatus Phaseolus USA Cover crop

Sorghum halepanse Johnson grass USA Forage crop

1 Presented at the International Symposium on Ecology of Biological Invasions, School of
Environmental Studies, Delhi University, Delhi, India, December 4-6, 2003

Accidental introductions

Many of the alien agricultural weed species have been accidentally introduced
as contaminants of crop seeds. Despite the Federal Seed Act, weeds continue
to arrive in the USA as seed contaminants. Similar contaminations of alien
plant species have been identified in many countries in the world. Soil-inhab-
iting species can be introduced by shipping soil or by soil attached to plant
material. Machinery and vehicles are often shipped from place to place with-
out cleaning. Depending on their uses, they may carry soil and plant material.
Historically, military equipment has resulted in several introductions of harm-
ful species, such as the golden nematode ( Globodera rostrochinensis) into the
USA [22].

Impacts of invasive species on society

Species inhabiting outside their historic areas of distribution often escape var-
ious checks, such as natural enemies, that normally limit their population
growth. They may impact native species, through predation, herbivory,
resource competition, aggression or hybridization [23]. They can displace and
even cause the extinction of unique variants or races, resulting in an irrepara-
ble loss of genetic diversity [24].
Invasive species have enormous impacts on our society including econom-
ic, social, and ecological aspects. According to a recent survey by the US
Department of the Rangelands in the West, western wildlands are being lost
from grazing land at a rate of 1,840 hectares per day to invasive plants such as
leafy spurge ( Euphorbia esula L.) and yellow starthistle ( Centaurea solstitialis
L.). In 1996, they indicated a 14% annual increase in area infested. If weeds
continued to spread at this rate, it was predicted that over 13 million hectares
of western wildlands were infested with weeds by the year 2000 [8]. Purple
loosestrife, a highly invasive species, can produce up to 2.7 million seeds per