"The Shrub Identification Book" by George W. D. Symonds
"The Handbook of Vermont Shrubs and Woody Vines" by L. R. Jones and F. V. Rand
"Trees and Shrubs of New England" by Marilyn J. Dwelley
"A Field Guide to Trees and Shrubs" by George A. Petrides
"Botany Everywhere" by Martin Michener (a revolutionary electronic-format guidebook for New England plants)