Fungi are primarily terrestrial, achlorophyllous, eukaryotic organisms that were at one time grouped with plants. Today, however, fungi are regarded as a monophyletic group more closely related to animals than plants and they occupy their own Kingdom (FIG. 3.1). Plesiomorphies shared with animals include the presence of chitin, food stored as glycogen, and, in the mitochondrial RNA, the bases uracil-guanine-adenine (UGA) code for the amino acid tryptophan (plants use UGG to code for tryptophan). The multicellular fungal body consists of filaments, called hyphae (sing. hypha), which together make up the mycelium or vegetative body of the fungus. From this simple organization, however, fungi can form many types of complex sexual and asexual reproductive structures, and they have developed adaptations that allow them to live in every habitat on Earth. Approximately 100,000 species of fungi have been described, but estimates

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