eFloras.org, from the Missouri Botanical Garden.
Find volumes for Flora of China, Moss Flora of China, Flora of North America and others at this site. URL is http://eFloras.org.

Guide to Standard Floras of the World, by David G. Frodin. (2nd ed., 2001, Cambridge University Press)
Marx Library QK45.2 F7 2001 (LC)
online: http://site.ebrary.com/lib/yale/Doc?id=10021935

Native and Naturalized Trees of New England and Adjacent Canada: A Field Guide 2006 location

AMC Field Guide to Mountain Flowers of New England 1977 location

Wild Edible Plants of New England: A Field Guide: Including Poisonous Plants Often Encountered 1981 location 

Orchids of the Northeast: A Field Guide 1997 location

Field Guide to Edible Wild Plants of Eastern and Central North America.1978 location

Medicinal Plants of North Africa by Loutfy Boulos 1983 location 1 location 2

Field Guide to Medicinal and Useful Plants of the Upper Amazon.1998 location

Atlas of Medicinal Plants of Middle America - Bahamas to Yucatan by Julia F. Morton 1981 location

Field Guide to Pacific States Wildflowers: field marks of species found in Washington, Oregon, California, and adjacent areas: a visual approach arranged by color, form, and detail.1976 location

Field Guide to Indiana Wildflowers. 2000 location

Field Guide to Common South Texas Shrubs.1997 location

Field Guide to Plants of Costa Rica. 2008 paper ed. location

Field Guide to Wild Flowers of Southern Europe by Paul Davies and Bob Gibbons.1993 location

Field Guide to Some Common Galapagos Plants.1970 location

Flora Hawaiiensis; the New Illustrated Flora of the Hawaiian Islands by Otto Degener.
volumes 1-5, 7 1946 location

Field Guide to the Aloes of Malawi. 2004 location

Field Guide to the Aloes of Rhodesia.1974 location

Field Guide to the Acacias of South Africa. 2008 location 

Field Guide to Palms in Papua New Guinea: with a multi-access key and notes on the genera. 2001 location

Field Guide to the Ferns & Lycophytes of Louisiana: including East Texas, Southern Arkansas, and Mississippi. 2011 paper ed. location

Field Guide to the Ferns and their Related Families of Northeastern and Central North America with a section on species also found in the British Isles and Western Europe.1963 location

Caribbean Reef Invertebrates and Plants: a field guide to the invertebrates and Plants occurring on coral reefs of the Caribbean, the Bahamas and Florida.1978 location

Field Guide to Poison Ivy, Poison Oak, and Poison Sumac: prevention and remedies. 2008 location

Wildflowers in the Field and Forest: A Field Guide to the Northeastern United States 2006 location 

Vascular Flora of Illinois: a field guide. 4th ed. 2014 paper ed. location

Wildflowers of Unalaska Island 2003 location 1 location 2

Important Plants of Northern Nimba County, Liberia. 2013 location

Genus Tulipa: Tulips of the World. 2013 location