Flora of Pennsylvania,
by Thomas Conrad Porter. Edited with the addition of analytical keys by John Kunkel Small.
Porter, T. C. (Thomas Conrad)., Small, J. Kunkel. (1903). Flora of Pennsylvania. Boston: Ginn & Company.
Porter, Thomas C. (Thomas Conrad), 1822-1901, and John Kunkel Small. Flora of Pennsylvania. Boston: Ginn & Company, 1903.
Warning: These citations may not always be complete (especially for serials).