Newcomb, Lawrence. Newcomb's Wildflower Guide: An Ingenious New Key System for Quick, Positive Field Identification of the Wildflowers, Flowering Shrubs and Vines of Northeastern and North-central North America. Little, Brown and Company, Boston: 1977.
Peterson, Roger Tory and McKenny, Margaret. A Field Guide to Wildflowers: Northeastern and North-central North America. Hougton Mifflin Company, Boston: 1968
Petrides, George A. A Field Guide to Eastern Trees: Eastern United States and Canada, Including the Midwest. Houghton Mifflin Company, Boston: 1988.
Uva, Richard H., Neal, Joseph C., and DiTomaso, Joseph M. Weeds of the Northeast. Comstock Publishing Associates, Ithaca: 1997.
(The links provide are to Amazon.com for ease of use, but the authors most whole-heartedly endorse patronizing locally owned book shops to fulfill your field guide procurement needs.)