botanical garden

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A place where plants are cultivated for scientific, educational, and ornamental purposes, often including a library, a herbarium, and greenhouses; an arboretum.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A place where a variety of plants are grown, primarily for scientific or educational reasons, but are normally open to the public, and include ornamental plants from around the world.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a facility where trees and shrubs are cultivated for exhibition