Leaves

Leaves are a type of block. They are abundant in normally generated maps, appearing on every tree, and are a renewable resource. Leaves have multiple textures, varying slightly in color; however, each individual leaf block will use the same texture on all six sides.

Leaves are available for use in Creative and Survival mode. They are often used in making plants, foliage, and tree houses. Leaf blocks are very weak, can be easily destroyed by hitting them with any tool, are extremely vulnerable to explosions and are highly flammable. As of Beta 1.2, leaves in snowy areas have a different texture. It is possible, but extremely unlikely for a leaf block to stay on fire forever after catching on fire.

Destroying leaves yields saplings 5% (1/20) of the time which can be planted by the player in order to grow new trees. Jungle leaves drop saplings 2.5% (1/40) of the time. Oak leaves also have a 0.5% (1/200) chance of dropping an apple.

As of Beta 1.7 leaves can be collected using Shears. Using shears collects the leaves with a single click (unless you are in air and/or underwater, which will make them almost instant to harvest using shears yet not as fast), making it faster than the sword. As of Beta version 1.8, player-placed leaf blocks no longer decay. Natural leaf blocks can be up to four blocks away from a log block and not disappear. Leaves can be destroyed faster than with your hands, but lose double durability when doing so. Other tools, except for shears, give little advantage over your hands.

Since the color of leaves can vary depending of biomes, some trees (on a border) may have more than one leaf color on the same tree.

Alpha
In Alpha, leaves would decay using an algorithm that checks whether it has a solid or leaf block underneath it or is adjacent to a solid block. If it doesn't, it must be connected to a leaf block that is also supported as long as it is no further than five blocks away from said support.

Beta
In Beta, leaves decay according to a simple formula: leaf blocks decay unless they are within 4 blocks of a log block, and connected to the log by other leaf blocks. Thus, harvesting the wood from a tree will cause the leaf blocks to vanish randomly one by one. Before Beta 1.7 leaves could not be harvested without mods, and since Beta 1.8, player or enderman placed leaf blocks will persist over time without decaying.

Bugs

 * When obtained using Silk Touch instead of shears, the several dropped leaf blocks cannot be stacked. This is likely due to "placed" and "check for decay" bits being dissimilar. Moreover, the leaves' tag would always be Oak leaves.
 * When sprinting on leaves, the particles that appear are gray, caused by the fact that they use biome tinting.
 * On the Xbox 360 Edition leaf blocks will not decay if there is snow on top of them, even if there is no wood block adjacent to them.
 * Leaves disappear when pushed by pistons.

Trivia
1.3.1 fixed it; you now get the block.
 * In "Fancy" graphics mode, leaves are marked as transparent, but in "Fast" graphics they are opaque. You can see the effect by trying to look through a tree while toggling the graphics mode.
 * In Beta, while hitting leaves, clouds and Snow cannot be seen behind the block you are hitting.
 * Occasionally, leaves will grow through other blocks, acting as though they are still connected to the tree. They may also completely replace blocks they try to grow into.
 * Leaves do not prevent a sapling from growing. As long as the five blocks above a sapling are either leaves or air, it will grow provided it has enough light.
 * Leaves can be supported by a different tree if the original has decayed, even if that means the new tree is of a different species (e.g. a birch tree can support spruce leaves after the original spruce has been cut down).
 * In the default textures, the leaf to air ratio is about 3:2 for normal/birch leaves, and about 9:5 for spruce leaves.
 * Leaves placed by the player will still drop saplings.
 * Leaves do not prevent Chests from being opened, even when running in "Fast" graphics mode. See Opacity.
 * Despite being highly flammable, leaf blocks cannot be used as fuel for a furnace currently.
 * Leaves do not cushion a player's fall at all and the player will take completely normal fall damage. This is also the same on either Fast or Fancy graphics.
 * Some trees seem to occasionally drop apples or saplings without being destroyed due to creation of leaf blocks not supported by wood.
 * As of 1.2.5, using the "pick block" key in creative will give the player the sapling associated with the leaves, instead of the actual block.
 * Breaking and letting leaves decay yields the same amount of saplings/apples.