Autumnnwood is a block of Wood with beige brown (or coffee-brown) bark and light brown wooden core from an Autumnwood-tree.
Three different kinds of Autumnwood-trees can be found in Forests, they are rather large trees most often with 3x3 blocks wide trunks, although not reaching the height of tall Cragwood trees. They have star-like beige-white Autumnwood Flowers amongst their leaves. Usually fallen leaves will gather on the ground under their foliage.
Autumnwood leaves can be either red Cinnamon Autumnwood Leaves, yellow-brown Citrus Autumnwood Leaves or brown Mocha Autumnwood Leaves; while fallen leaves will always turn into Mocha Autumnwood Leaves when picked up.
The only places to find Autumn Leafi Leafs are under Autumnwood-trees or on tree-tops of Autumnwood-trees with Mocha Autumnwood Leaves. If you place Citrus or Cinnamon Autumnwood Leaves somewhere to creat an arena only ordinary Leafies will spawn. At night Night Leafies might regularely spawn on all kinds of Autumnwood Leaves.
Beehives made of Beeswax can sometimes be found in treetops of Autumnwood-trees, and currently (R25 in November 2015) they will also "grow" slowly from Queen Bees that will spawn from time to time on Autumnwood or on Autumnwood Leaves of any kind. You can also place Queen Bees on Autumnwood and/or Autumnwood Leaves yourself to grow Beeswax.
As of now there are no Saplings for Autumnwood-trees to be planted by players.
Autumnwood as well as Autumnwood Leaves can also be corrupted with Corrupt Bombs. Corrupted Wood placed directly next to Autumnwood (touching it) will turn it into Corrupted Wood too. This will make Leaves and Wood into Fuel of much higher quality.
When purifying these blocks of Corrupted Wood and Leaves again, (as of R25 in November 2015) they will turn into Cragwood and Cragwood Leaves though, even if they were Autumnwood and Autumnwood Leaves before being corrupted.