Problems preserving attribute data while merging fields in shapefiles

To all,

Currently, I have old datasets(shapefiles) that contain a plant code #
field in the attributes table.  I have successfully merged in a table
with spp. names to correspond with the plant code #'s.  During this
process my attribute data is resorted and I lose continuity with other
attribute data. (I'm using the (sp) and (maptools) libraries to
execute read/write Poly/Point shape functions.)  While merging, how do
you maintain continuity between all of the other fields in your
attributes table?

Thank-you for your time and help,
Levi

Research Assistant
Dept. of Watershed Sciences
Utah State University
5210 Old Main
Logan, Utah 84322
(740)-591-1750
LeviDRose at gmail.com