This function check which species (both plants and
animals) are considered "invaders" somewhere in the
world. For that end, it checks GISD
(http://www.issg.org/database/welcome/) and returns a
value, either "Not in GISD" or the brief description
presented in GISD.
Note that the webpage contains more information. Also
note that the function won't tell you if it's exotic in
your area, a lot of exotic species are not considered
invaders (yet).
As expected, the function is as good as the database is,
which I find quite reliable and well maintained. The
database is also able to recognize a lot (but not all) of
the species synonyms.