GardenNet Guide to Gardens of the USA
American Association of Botanical
Gardens and Arboreta
Arnold Arboretum of Harvard University Boston, Massachusetts
Boyce Thompson Southwestern Arboretum
Phoenix, Arizona
Black Hawk County Arboretum Waterloo, Iowa
Holden Arboretum Kirtland, Ohio
Maplelawn Garden Ottawa, Canada
Missouri Botanical Garden
St. Louis, Missouri
Royal Botanical Gardens -- Ontario, Canada