You can control the search with the two buttons below the Query
box. If you leave it as the default, your search is limited
only to "valid names". This means that the location data,
synonym data, etc are not searched. Only the lines starting
with "N: +" are searched.
If you click on the other button, "Show all matching entries",
then all fields will be searched. So to find all plants from the
USA, click "Show all matching entries", and search for "USA".
This also works for finding particular authors, publications, etc.
-- Rick