"I believe that mycelium is the neurological network of nature. Interlacing mosaics of mycelium infuse habitats with information-sharing membranes. These membranes are aware, react to change, and collectively have the long-term health of the host environment in mind. The mycelium stays in constant molecular communication with its environment, devising diverse enzymatic and chemical responses to complex challenges." ― Paul Stamets, Mycelium Running: How Mushrooms Can Help Save the World
The mycelium is the part of the mushroom you usually do not see. Most of it is found distributed throughout the soil, consisting of a mass of branching, thread-like structures (known as hyphae) which absorb nutrients and decompose organic materials. The mycelium can be exceedingly small or may form a colony of massive proportions.
Is this the largest organism in the world? This 2,400-acre (9.7 km2) site in eastern Oregon had a contiguous growth of mycelium before logging roads cut through it. Estimated at 1,665 football fields in size and 2,200 years old, this one fungus has killed the forest above it several times over, and in so doing has built deeper soil layers that allow the growth of ever-larger stands of trees. Mushroom-forming forest fungi are unique in that their mycelial mats can achieve such massive proportions.
—Paul Stamets, Mycelium Running