Armillaria solidipes, also called the honey mushroom, is the largest organism in the world. The largest reported mushroom found in the Blue Mountains in Oregon, USA, measures 3.8 km across. The fungus colony is also over 2,400 years old, making it one of the oldest organisms in the world as well. The large clumps of mushrooms that appear above ground are the fruiting bodies of much larger organisms. They consist mainly of black bootlace-like rhizomorphs that spread out below the surface in search of new hosts, and underground networks of tubular filaments called mycelia.