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 other blocks except Grass, whereas Grass can't spread to Mycelium in turn. 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. This block seems to emit some sort of particle-like substance much like the ones in The Void.