Podzol

Podzol is a dirt-type variant block that appears in the Mega Taiga biome. Similarly to grass blocks and mycelium, it can only be obtained by digging it with a Silk Touch-enchanted tool; otherwise, it drops dirt instead.

Podzol appears to share traits with mycelium, in that it allows mushrooms to be placed on it no matter the light level, thus allowing the growing of giant mushrooms. However, unlike mycelium, it does not spread to adjacent dirt blocks. Saplings and other plants can be placed on it. Podzol seems to be a grass block with dead leaves and moss scattered on top of it.

Trivia

 * Unlike other similar blocks, podzol will never spread to dirt blocks, nor will it turn into dirt if a solid block is placed on top of it, no matter how long the block remains on top of it. This is because podzol is a type of soil, and has the same Block ID as dirt, just a different damage value.
 * Podzol appears to be comprised mainly of small grass scraps, dead leaves and moss.
 * Grass cannot grow on podzol.
 * In real life, podzol is the type of soil usually found in coniferous forests in wet, cold areas as well as warmer areas.
 * All flowers can be placed on top of podzol.
 * Podzol can be picked up by Endermen.