Royal Botanic Gardens, Kew It's considered the world's largest collection of living plants with more than 50,000 of them across 300 acres of dedicated land, including many species you'd never expect to find in England. For that, you have the climate-controlled Princess of Wales Conservatory to thank.

1. New York Botanical Garden, Bronx, New York. The largest in any city, this 250-acre wonder has 50 specialty gardens and collections comprising more than one million plants, plus 30,000 trees and a Victorian-era glasshouse.

The United States Botanic Garden is the oldest continuously operating public garden in the United States. The Garden is rooted in the nation's heritage. During the late 18th century, George Washington had a dream of a national botanic garden and was instrumental in establishing one on the National Mall in 1820.

The world's first university botanical garden was created in Padua in 1545, which makes the Botanical Garden of Padua the oldest surviving example of this type of cultural property.