A fungus (pronounced /'f??g?s/) is a eukaryotic organism that is a member of the kingdom Fungi (pronounced /'f?nd?a?/ or /'f??ga?/). The fungi are a monophyletic group, also called the Eumycota (true fungi or Eumycetes), that is phylogenetically distinct from the morphologically similar slime molds (myxomycetes) and water molds (oomycetes). The fungi are heterotrophic organisms possessing a chitinous cell wall, with most species growing as multicellular filaments called hyphae forming a mycelium; some species also grow as single cells. Sexual and asexual reproduction of the fungi is commonly via spores, often produced on specialized structures or in fruiting bodies. Some have lost the ability to form reproductive structures, and propagate solely by vegetative growth. Yeasts, molds, and mushrooms are examples of fungi. The discipline of biology devoted to the study of fungi is known as mycology, and is often regarded as a branch of botany, even though fungi are more closely related to animals than to plants. Occurring worldwide, most fungi are largely invisible to the naked eye, living for the most part in soil, dead matter, and as symbionts of plants, animals, or other fungi. They perform an essential role in ecosystems in decomposing organic matter and are indispensable in nutrient cycling and exchange. Fungi may become noticeable when fruiting, either as mushrooms or molds. They have long been used as a direct source of food, such as mushrooms and truffles, and in fermentation of various food products, such as wine, beer, and soy sauce. More recently, fungi are being used as sources for antibiotics used in medicine and for various enzymes, such as cellulases, pectinases, and proteases, important for industrial use or as active ingredients of detergents. Fungi are also deployed as biological agents that control weeds and pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides that are toxic to animals including humans. Fruiting structures of a few species are used recreationally or in traditional ceremonies as a source of psychotropic compounds. Fungi can cause deterioration of manufactured materials and buildings, represent significant pathogens of humans and other animals, and losses due to fungal diseases of crops (e.g., rice blast disease) or food spoilage can have a large impact on human food supply and local economies. The fungal kingdom encompasses an enormous diversity of taxa as shown by the various morphologies (ranging from amoeba-like protists and single-celled aquatic chytrids to large mushrooms), ecologies, and life history strategies. However, only limited and incomplete information is available for most species; the biodiversity of Kingdom Fungi has been estimated at approximately 1.5 million species, although only about 5% of all species have been formally classified. Ever since the pioneering 18th and 19th century taxonomical works of Carl Linnaeus, Christian Hendrik Persoon, and Elias Magnus Fries, fungi have been classified according to their morphology (e.g., characteristics such as spore color or microscopic features) or physiology. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, which has sometimes challenged the historical groupings based on morphology and other traits. Phylogenetic studies published in the last decade have helped shape the classification of Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla.