Missouri Botanical Garden (U.S.)
Credit: Eddie Brady / Getty Images

Founded in 1859 by an English botanist, the 79-acre garden is one of St. Louis' biggest attractions, in part thanks to Seiwa-En, the the world's largest Japanese garden. Other cultural displays include Victorian, Ottoman, and Chinese gardens, and the tropical plants below the garden's famous Buckminster Fuller geodesic dome known as the Climatron. The Missouri Botanical Garden is at the forefront of plants science, including a partnership with Kew Gardens to compile a checklist of the world's flora species know as The Plant List. Their herbarium recently hit 6.5 million species.
[missouribotanicalgarden.org]