mycélium

Mycelium, also spelled mycélium, is the vegetative part of a fungus, composed of a vast network of threadlike filaments called hyphae. These hyphae grow and branch to form a mass that extends through or over the substrate the organism colonizes, such as soil, wood, or decaying organic matter.

Hyphae secrete extracellular enzymes that break down complex polymers outside their cells, enabling the fungus to absorb nutrients. Mycelium plays a central ecological role as a decomposer, breaking down organic material and recycling nutrients. It also forms mutualistic associations with plants, most notably mycorrhizae, where fungal hyphae connect with plant roots to boost water and nutrient uptake in exchange for carbon from the plant.

Growth can produce specialized structures such as rhizomorphs—thick, cordlike filaments that transport water and nutrients over distance—and, in some species, sclerotia, hardened masses that help survive adverse conditions. Reproduction typically occurs through fruiting bodies, such as mushrooms, which generate and release spores that disperse to colonize new substrates. The mycelial stage is often inconspicuous but fundamental to the fungus’s lifecycle and ecological functions.

Mycelium is important for ecosystems by accelerating decomposition, facilitating nutrient cycling, and improving soil structure. For humans, mycelia are cultivated for edible mushrooms and explored for applications in food ingredients, pharmaceuticals, bioremediation, and sustainable materials. As with any fungal group, some species produce toxins or allergens, so proper identification, handling, and safety practices are important.