Leaves are a kind of currency that can be used to purchase items from the Leaf Exchange. Those with upgraded accounts can collect two per day by visiting the Pear Tree. They can also be purchased from other users via the Shop Search. There are 9 different colors of leaves, with each color having its own allotted point value (called "Leaf Points"). Leaves you own can be found in your inventory under "Leaves", or in your "Leaf Bag" (found under world).
On September 24th, 2009 it was announced that the leaves for the pear tree would be getting redrawn. Two designs were put to a vote; the current design (which resembles an oak leaf more than a pear leaf), and the other a more "realistic" pear leaf design show to the right. The less realistic design won, and is what we now see on the site.