Mushroom Forest

Mushroom Forests are very large biome, located 125 to 200 meters below sea level.

They are characterised by large tree-like mushroom structures and brownish grass on the ground.

Mushroom Trees
The Mushroom Trees consist of a tall stem with mushroom caps protruding branch-like from them. All trees grow to different heights and can grow up to 100 meters tall. The largest Mushroom Trees often have basalt clusters at the top. Some of them will also grow lithium on their bark.

You can break off the mushroom caps by hitting them with the knife or colliding with them while driving a submarine, causing them to slowly drift to the ground.

Speculation
There is currently one massive Mushroom Tree in the game. By glitching through the wall, it can be seen that the tree has an interior that will likely be accessible by the player in future builds. The interior has already been designed, it seems.

By entering BIOME TREE into the console, players can currently teleport themselves to the tree. The mere fact that this command exists proves the importance of the tree.

Resources

 * Diamond
 * Exosuit Fragment
 * Gold
 * Lithium

Fauna

 * Airsack
 * Bone Shark
 * Jellyray
 * Reefback

Flora

 * Ball Cluster
 * Barnacle Suckers
 * Blue Cluster
 * Small Fan Cluster
 * Tree Mushroom