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.