The Fungus Kingdom is smaller than the Animal Kingdom but probably larger than the Plant Kingdom. E.O Wilson, in his 1992 book "The Diversity of Life", stated that there are about 1,413,000 described species of organisms on earth. Of these 1,002,000 are animals (751,000 of which are insects), 248,000 are higher plants, 69,000 are fungi and the remaining 94,000 are scattered among several other smaller kingdoms. However these totals are based on described species and it is well known that most groups of smaller organisms are still poorly studied. For example, zoologists have attempted to estimate the actual number of insect species on earth, including projections for newly described ones, and have come up with a conservative estimate of five to ten million, compared with the currently described 751,000. Similar estimates for the fungi set their number at about 1,500,000. Certain groups of organisms, such as higher plants and vertebrate animals, have been fairly well documented and are no longer being described at the rate occurring with small organisms like insects and fungi. As this gap in our knowledge is gradually closed we will finally be able to say with certainty that the Fungus Kingdom is larger than the Plant Kingdom.

Not only are fungi numerous they are also very diverse. Just how diverse we are just beginning to discover. Until recently fungi were classified into several classes, orders, and families based on their outward appearance. If two fungi looked alike they were considered to be related. This provided people who wished to learn about fungi a solid framework upon which to build their knowledge. Since the early 1990's scientists have been exploring the relationships among fungi by comparing the similarities of their DNA. As this work becomes more and more sophisticated we are discovering that the fungi are far more diverse in their ancestry than anyone had imagined. We are also finding out that species that look alike may not necessarily be related and, conversely, that ones that do not look alike may be close relatives. On these pages we are faced with the task of presenting the diversity of fungi as they will be seen by the naturalist and collector, and of integrating these observations into a classification scheme acceptable to most of today's mycologists.

Levels of classification

Schemes for classifying fungi all follow a formal hierarchy specified in the The International Code of Botanical Nomenclature. This set of rules governs how fungi are named and how we are to deal with disputes over which is the correct name for a particular fungus. For example, if two mycologists independently name a new species, something which happens more often than we would like, the ICBN requires one of these names to have priority over the other and provides the guidelines for determining which of the two will prevail.

The ICBN also specifies the levels of classification that should be used for fungi and the form of the names we apply to each level. These level-specific names are recognized by their endings. For example, the name of a family of fungi will always end in -aceae, such as the Sordariaceae, Agaricaceae or Pucciniaceae. Other levels have other endings. The following is a list of these levels and their endings:

  • Kingdom
    • Subkingdom (no ending specified)
      • Phylum (-mycota)
        • Subphylum (-mycotina)
          • Class (-mycetes)
            • Subclass (-mycetidae)
              • Order (-ales)
                • Suborder (-ineae)
                  • Family(-aceae)
                    • Subfamily (-oideae)
                      • Genus (no ending specified)
                        • Subgenus (no ending specified)
                          • Species (no ending specified)
                            • Subspecies (no ending specified)

All names from kingdom down to genus begin with a capital letter. Species epithets always are in lower case. The name of a species is never written without its genus. Thus we may call the fly agaric Amanita muscaria and never just muscaria. Note in this example that the generic name begins with a capital "A" while the species epithet begins with a lower case "m". In addition to these conventions, names of genus and species are always italicized or underlined while those above genus are not. In the above example Amanita muscaria belongs to the family Amanitaceae in the order Agaricales.

To start, we have divided the fungi into two groups, those that are accepted by all mycologists, molecular and traditional, as belonging to the Fungal Kingdom and those that look like fungi but are not members of the Fungal Kingdom. The reasons for these two groups are explained in the discussion pages for both groups.