Mycelium is the vegetative part of a fungus consisting of a mass of branching threadlike hyphae that exists below the ground or within another substrate. It is through the mycelium that a fungus absorbs nutrients from its environment. It does this in a two stage process. Firstly the hyphae secrete enzymes onto the food source which breaks down polymers into monomers. These monomers are then absorbed into the mycelium by facilitated diffusion and active transport. Mycelium is also a vital component in many ecosystems in that it helps increase the efficiency of water and nutrient absorption of many plants and also is vital to the decomposition and breaking-up of plant material to form the organic part of soil and to release carbon dioxide back into the atmosphere.
The mycelium of the Honey mushroom, Armillaria bulbosa (= A. gallica), with its clones has been estimated to extend over 15 hectares (37 acres) with a protoplasmic mass of 10,000 kilograms (22,000 pounds) and an age of 1500 years (Smith et al., 1997). At this size and age, A. gallica is the largest and oldest living thing on the planet.
The familiar hat-like head and stalk of mushrooms are in fact reproductive structures of ascomycetes and basidiomycetes fungi, and are not classified as mycelium.
See also: mycorrhiza, carbon cycle, sclerotia
Reference
- Smith, M., Bruhn, J., and Anderson, J. 1992. The fungus Armillaria bulbosa is among the largest and oldest living organisms. Nature 356:428-431.
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