definition of mycelium
Mycelium as seen under a log. Mycelium is the vegetative part of a fungus, consisting of a mass of branching, thread-like hyphae. The mass of hyphae is sometimes called shiro, especially within the fairy ring fungi.ycelium is an important food source for many soil invertebrates. Mycelium, like fungus, can be considered a mass noun, a word that can be either singular or plural. The term mycelia, though, like fungi, is often used as the preferred plural form. Sclerotia are compact or hard masses of mycelium.