usually referred to simply as Kew Gardens,

At almost 5000 square metres in area, and holding the title of
Largest Victorian Glasshouse in the World, the Temperate House
really is vast (twice the size of the nearby Palm House). At the
centre of the Temperate House is the Chilean wine-palm, which at a
heady 16 metres, towers into the record books as the World’s largest Indoor Plant

from Wikipedia