mycelium(redirected from Mycellium)
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the vegetative body of a fungus; it consists of fine (1.5–10 microns in diameter), branched filaments (hyphae). It develops within a substrate or, less frequently, on its surface. The mycelium may be noncellular (Phycomycetes) or multicellular (Ascomycetes, Basidiomycetes, and Fungi Imperfecti). The mycelium cells of Phycomycetes, Ascomycetes, and Fungi Imperfecti are always haploid. In Basidiomycetes the primary mycelium that develops from spores is haploid; further in its development it becomes diploid owing to its merging with the mycelium of the other sex (heterothallism) or the convergence of the nuclei in the anastomosing cells (homothallism). Vegetative reproduction of fungi is accomplished by fragments of the mycelium.