Maple

A maple was a type of tree native to Earth which was used to, among other things, make maple syrup.

Clara Oswald left a maple leaf inside 101 Places to See, a book that she owned from around 1998 to 2013. She referred to it as "the first page." When, in 2013, the Eleventh Doctor visited, he stared at the leaf questioningly, and licked it. (TV: The Bells of Saint John)

Behind the scenes
The tree is not actually named in Bells, but the leaf is prominently displayed and obviously that of a maple.