Mycelium

Mycelium is a new block type found in Mushroom Biomes. It acts like dirt, and when harvested with a shovel will yield one dirt block. It slowly spreads to bare dirt blocks .Saplings and Flowers can not be placed on Mycelium, but Mycelium can spread beneath them, which causes them to drop as items from the spot. There are some effects for the top of Mycelium blocks which look like tiny spores being released constantly from the surface. Mooshrooms will spawn on it. Mycelium is also the only block on which mushrooms can stay when an adjacent block is updated despite a light level that is too high for the Mushroom to remain.

Trivia

 * In order to get Mycelium out of a Mushroom Biome, you may need to use Pistons or an Inventory Editor.