Leaves

Leaves generate as a part of trees. They need logs to stay, and if there isn't any, they decay. When the decay, they have a chance to drop 0-1 saplings, respectively to the type of leaf and tree, or 0-1 apples.

Obtaining
Sheer them with sheers.

When punched they can also have chances of dropping the sapling or apple.

Usage
Some people use them as hedges on servers to make things look nice.

Trivia

 * The reason the bug of the leaves looking like one pile has came up several times is because MCE had to change the leaves code when updating. Now, he know what piece of code does that, so it shouldn't happen in the future.
 * MCE decided to have the leaves as "null blocks", which means you can walk through them. No more tree hopping.