Some Autumnwood-trees are covered with red-colored Cinnamon Autumnwood Leaves, others with yellow-brown Citrus Autumnwood Leaves, and some with brown Moccha Autumnwood Leaves.
The ground under Autumnwood-trees is often covered with Fallen Leaves; if you pick them up, they will all turn into blocks of Moccha Autumnwood Leaves.
Blocks of Autumnwood leaves can be harvested/pulled with your arctek-gauntlet without needing any Power Cells. If you use Stone Mining Cells or better to pull leaves, these stronger Power Cells will not even lose durability.
In Creativerse tree leaves will not decay / vanish by themselves when you "cut" down the stem of the tree nor if you take away all the wood-blocks that the tree is made of. Instead the blocks of leaves (as well as all Flower-blocks, Beeswax, Vines, etc.) will prevail and float in the air until you take them down manually or use Excavators on them to collect at least half of them.
You can of course also throw Explosives at leaves and/or burn them. As leaves are flammable, burning them might work overly well in warm to hot environments. So beware of forest fires that will also burn down all the wood and Tallgrass! Spreading fires can be stopped by claiming the area and disabling the fire spreading option for the claims or by world owners by disabling the fire spread (fire sim) option for their gameworlds.
On the other hand burning attempts might stay below expectations in cold environments. Simple torches cannot even set fresh leaves aflame in snowy biomes (as of R25 in November 2015).
One block of Autumnwood Leaves can be processed into 4 blocks of Shredded Leaves in the Processor. Taking or crafting Shredded Leaves is one of the unlocking requirements for the crafting recipe of three types of colored carpets. Shredded Leaves are an important crafting ingredient for all kinds of Beds and easierly catch fire than blocks of fresh Leaves when being placed.
All kinds of Autumnwood Leaves can be placed as solid blocks for decoration and can also be used for building; however they can make creatures spawn, like ordinary Leafies, Autumn Leafies (more rarely) during the day, and also Night Leafies in darkness.
All kinds of Autumnwood Leaves can be used as Fuel for the Forge, however 4 blocks of leaves are needed and used up for each melting-/hardening-process. Also each melting-/hardening process in the forge will take quite long when you use leaves as fuel.
All kinds of Autumnwood Leaves can be corrupted into Corrupted Autumnwood Leaves by using Corrupt Bombs on them. By that they will turn into better fuel, but they have to be picked up using Lumite Mining Cells, which will reduce the durability of the Mining Cells quite a bit (just like pulling all other kinds of corrupted blocks). Corrupted Leaves cannot be processed into Shredded Leaves.
Since R43, these corrupted leaves will turn into common Corrupted Leaves when picked up (that will turn into Cragwood Leaves when being purified). By purifying Corrupted Autumnwood Leaves (that have not been picked up yet) with either Healing Beacons or Purification Bombs, they will all transform into red Cinnamon Autumnwood Leaves instead of into the specific subtypes of Autumnwood Leaves (Cinnamon, Moccha and Citrus Autumnwood Leaves, no matter which type they had been before being corrupted).
You can plant Queen Bees on Autumnwood Leaves to grow Beeswax, which will take ca. 3,5 hours (real-life time). Currently (R25 in November 2015) you cannot grow Autumnwood-trees from Saplings, and no more Autumnwood Flowers than initially existed will slowly grow on Autumnwood Leaves (different from Blue, Red and Yellow Flowers). You can obtain Autumnwood Flowers from Autumn Leafies occasionally though, either as a loot or pet-harvest.