What Is Mycelium?

When most people think of fungi, they picture mushrooms, but these are merely the reproductive structures. The true organism is mycelium: a web of microscopic tubular cells (hyphae, typically 2-10 micrometres in diameter) that penetrate soil, wood, and other substrates. A single cubic centimetre of forest soil can contain 8 km of hyphae. Mycelium serves as nature primary decomposer, breaking down dead organic matter and recycling nutrients. It also forms mycorrhizal networks with plant roots — the "Wood Wide Web" — through which trees exchange nutrients, water, and even chemical warning signals about pest attacks. About 90% of land plants depend on mycorrhizal fungi. Mycelium is increasingly used in technology: as a sustainable alternative to leather, packaging foam, building insulation, and even as a substrate for growing meat alternatives. The largest known organism on Earth is a honey fungus (Armillaria ostoyae) mycelial network in Oregon covering 9.6 square kilometres.