Tree Leaves will remain the same size during sapling growth, however, they may change shape or size when the tree's first pair of branches form. Once a tree has fully grown, leaves will cease to grow larger and can only be affected if part of the tree breaks or dies. And if the branch below a leaf is broken off or the tree dies, in general, all the leaves affected by this will immediately cease to be anchored and will fall through the ground. In certain cases where limbs of the tree fail to load, it can create a "floating" effect on the affected leaves when there is no other actual change.
Only few trees have unique leaf materials; some of which are Zombie Trees with the Granite material, Lava Trees with the Concrete material, Cavecrawler Trees with the Foil material, and Cherry Trees with the Pebbles material on its leaves. During the 2016 Halloween and 2017 Halloween events, all types of trees lost their leaves, as an apocalyptic feature.
Some time during the Alpha and Beta Testing Stage, if timed right, a player can grab a tree leaf, and can show it to other players. Despite of this glitch having no significant impact to the game, it was still patched and people can no longer do it.