Mycelium will grow on any dirt block in an area where other mycelium blocks exist, even if the dirt blocks have a sapling or another plant on it (although the plant will fall off as soon as mycelium appears). Mycelium will spread to adjacent dirt blocks, as long as enough Light reaches the block. Its spread can be stopped by creating an obstruction to the mycelium's expansion, such as a two-block change in terrain height or a non-dirt block.
Small "spore-like" particles appear above the surface of mycelium blocks. It is the only block besides giant mushroom blocks and dirt blocks that appear on the surface of the mushroom island.
- Mycelium was first added in the first Beta 1.9 release, but it was only usable in Creative mode.
- As of 1.2.4, mycelium is the only block on which players can spawn mushrooms while in sunlight.
- They were added to Pocket Edition in the 0.9.0 update, along with mushroom island biomes.