The kingdom Fungi includes several phyla, here called the "True Fungi". They are all heterotrophic, meaning they do not carry out photosynthesis, are generally composed of more than one cell and have cell walls containing at least some chitin or chitosan, large polysaccharide molecules composed of repeating units of the amino sugars glucosamine and N-acetylglucosamine. Organisms having photosynthesis have never been discovered in this kingdom. Except for the two small groups of fungus-like organisms that are not true fungi treated on the previous page anything that looks like a fungus is likely to be a true fungus.
Mycologists generally recognize four phyla of true fungi, the Chytidiomycota, the Zygomycota, the Glomeromycota and the Dikarya. In practice these are not difficult to distinguish.
The Chytridiomycota usually have a very simple organization, often being one-celled, and are the only true fungi producing motile spores.
The Zygomycota are varied but reproduce sexually by means of zygosporangia. Most Zygomycota have coenocytic hyphae (few or no septa).
The Glomeromycota resemble the Zygomycota but never produce zygosporangia and consistently form arbuscular mycorrhizae with higher plants.
The Dikarya, a huge subkindom outnumbering all other fungi combined, is characterized by the production of meiospores (products of sexual reproduction) in asci and basidia. Hyphae of the Dikarya are always septate. The phylum contains most of the organisms people recognize as fungi.