Non-native plants are a conspicuous part of the Texas
landscape, from lawns and roadsides to relatively undisturbed natural
communities. Currently, Texas provides
habitat for more than 850 of these species, which are native to various parts
of the world, including Asia, Europe, and Central America and South
America. They grow spontaneously in
Texas, outside of cultivation (they are naturalized). Many are invasive and pernicious weeds,
crowding or replacing native flora; others appear more benign, mostly
restricted to lawns, roadsides, and other sites that are heavily disturbed, or
else they are known only from one or a few places. Of course, some of the most recently arrived species in our state
may ultimately become noxious invasives.
Many are naturalized and irretrievably established in Texas, and the
future surely will see many more extra-North American species become
established and abundant.
What is an “invasive species”?
As
legally defined, an invasive species is “An alien species whose introduction
does or is likely to cause economic or environmental harm or harm to human
health …. ‘Alien species’ means, with
respect to a particular ecosystem, any species … that is not native to that
ecosystem.” Alien species are also
known as exotic, non-native, introduced, or non-indigenous species, and the
term noxious or nuisance is sometimes used instead of “invasive”
when these organisms cause harm.
Although they are “natural” and because they can spread very quickly ––
or very slowly, over years or even decades --
invasive species cause a range of problems. They can
• threaten the survival of native plants and
animals
• interfere with ecosystem functions
• hybridize with native species, resulting in
negative genetic impacts
• spread easily in today’s era of global
commerce
• be difficult and costly to control
• impede industries and threaten agriculture
• be a significant drain on the economy
• endanger human health
(from "Invasive
Species of Texas," Union of Concerned Scientists,
2002)
Four
terms provide a general description of the major categories of non-native
plants in our flora: cultivated, persisting, waif, and naturalized.
Comparative definitions are provided for seven related terms that
describe the non-native origin and floristic integration of vascular plant
species in North America: adventive, alien, escaped, established, exotic, introduced, and non-native. (G.L. Nesom. 2000. Which non-native plants are included in floristic accounts? Sida 19:189-193.
Another set of terms and definitions
describing degrees of naturalization is given by Brett Serviss at Non-native Woody Plants of Arkansas: non-native, waif, adventive,
spontaneous, escaped,
established, naturalized,
invasive.