In biological classification, fungi belong to the taxonomic kingdom Fungi.
The kingdom includes mushrooms, yeasts, molds, and many microscopic or aquatic organisms. Fungi are eukaryotes, meaning their cells contain nuclei, and they obtain nutrients by absorbing dissolved organic material rather than making food through photosynthesis.
Fungi were once commonly grouped with plants because both are usually immobile and often grow in soil. Modern biology separates them: fungal cell walls contain chitin, while plant cell walls mainly contain cellulose. Molecular evidence also shows that fungi are evolutionarily closer to animals than to plants.
A common mix-up is confusing the kingdom Fungi with a visible mushroom. A mushroom is usually only the fruiting body of a larger fungus, whose main body consists of threadlike hyphae forming a network called mycelium. Fungi are also major decomposers and form important partnerships with plant roots.