A Tree Grows in the Courtyard | The Medieval Garden Enclosed | The Metropolitan Museum of Art, New York:
"Visitors to The Cloisters may have spied the top of a large oak tree just above the wall at the postern gate entrance. This white oak grows in a courtyard enclosed by the ramparts, which also include maintenance passages, storage, an education workshop area, and garden workspaces.
Quercus alba, the white oak, is a common and long-lived North American hardwood. The bark gives the tree its name, though it is usually light gray rather than white. Oak timber is water resistant, strong, elastic, and dense, qualities that have led to a multitude of uses ranging from shipbuilding to supports for panel paintings (see “The Garden in Heraldry: The Great Oak of the Forest,” December 8, 2011). In addition to its timber, the oak’s bark is used in cork making, in tanning, and as a dyestuff. It also has several medicinal applications."