Leaves

Instead of depicting limbs and individual leaves on trees, The Blockheads represents them as special blocks called leaves. They are also referred to as "branches" in the tutorial.

Appearance
Leaves vary in appearance depending on the season and type of tree they're associated with. All are mottled in color and partially transparent. Most leaves are some shade of green most of the time.

Where Found
Leaves are always associated with a tree and are the first part of a tree to spawn. While their pattern can overlay a block of tree trunk, it does not make it a block of leaves. They will spawn and despawn in relation to the growth of their tree.

Dead leaves (the sparse black lines are distinctive) representing trees that died before growing further can sometimes be found along the ground in arctic climates.

Effects
Leaves prevents the placement of other blocks in that space.

Fruit will only spawn on leaves, not on leaf-covered trunk. The block immediately above a tree's trunk is also non-spawning.

There must be an uninterrupted line of leaves to a tree's trunk or they will despawn. When they despawn, they will drop anything attached to them and possibly a stick.

Leaves can be climbed on. The leaves of a dead tree can be climbed on but cannot be harvested.

The leaves of some trees change color and even transparency based on the season.

Uses
A block of leaves may produce a stick when it despawns. It will almost certainly produce one if deliberately harvested, and tends to produce three if a machete is used.

Leaves can be climbed on and may provide an alternative to ladders in some situations.