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KINGDOM FUNGI

The Fungi have been recognized as a separate kingdom since the work of Whittaker (1957 and 1959).  For a time Margulis and Schwartz (1982 and 1988) insisted that the fungi were derived from a lineage that never had flagella.  However, the tide of evidence from molecular phylogentic studies demonstrated that the fungi evolved from a flagellated line [see Tudge (2000) and Baldauf (2003) for a synopsis of the work].  Indeed, that the chytrids were part of that line and that the fungal clade was part of a larger clade called the opisthokonts (animals + fungi in the Unikonta), a group that includes the choanoflagellates and the metazoans, suggests that the fungi and animals are "cousins" (Baldauf and Palmer 1993; Baldauf 1999; and Patterson 1999).  Margulis and Schwartz (1998) still maintain that the fungi are a kingdom of conjugating taxa, and, therefore, continue to exclude the chytrids.

The most surprising change in fungal taxonomic systems in recent years has been the inclusion of the intracellular parasites of insects and fish called microsporideans (Edlind et al., 1996; Keeling and Doolittle 1996; Fast et al. 1999) based on protein gene comparisons.  The unexpected feature of this association was the apparent primitive nature of the microsporideans based on ssu rRNA studies.  Indeed, they were usually given at the base of the eukaryote tree along with other putative primitive forms as Giardia and the parabasalids, especially in Archaezoa scenarios (Cavalier-Smith, 1983; see my discussion on this).  However, Germot et al. (1998) established that the microsporidians had evolved from a mitochondriate ancestor, and Hirt et al. (1999) then demonstrated their clear affinities with the opisthokonts, particularly the fungi.  Since then, independent lines of research have established their association with the fungi (e.g. Fast and Keeling 2001; Keeling 2002; Sokolova et al. 2003; and Ragan et al. 2003).  Keeling (2003) argues that the microsporidia are not primitive at all, but evolved from a zygomycete ancestor.  Clearly, the microsporidians are fungi; however, their particular location within the kingdom is not clear.  Thus, I have designated them Incertae Sedis.

This system of typical fungal taxa (zygomycetes, ascomycetes, and basidiomycetes) is an adaptation of Hudson (1984) and generally follows the systems of Margulis and Schwartz (1988 and 1998), and Alexopoulos and Mims (1979, 1996).  The relationships of the phyla can be seen in a cladogram of relationships based on mitochondrial DNA sequences by Lang.  Schussler et al. (2001) demonstrated that the arbuscular mycorrhizal (AM) fungi, formerly in the order Glomerales of the Zygomycota, are monophyletic and distinctly different (based on ssu r-RNA comparisons) from all other fungal taxa, and they defined a new phylum, Glomeromycota, for them.  Their phylum-level status has been confirmed by other studies, particularly Lutzoni et al. (2004).  Schussler et al. (2001) and Lutzoni et al. (2004) also show that the Zygomycota and the Chytridiomycota are paraphyletic and will have to be revised into as many as 4 and 2 phyla, respectively.  

The form taxa (Form-Phyla, etc.) of the older taxonomies (e.g. Bold et al. 1987 and Alexopolous and Mims 1979) are not natural and have been sorted out according to their lineages.  These include some of the non-sexual fungi, forms in which sexual reproduction has become lost or significantly modified such that meiosis doe not occur.  Others are chimeroid organisms called lichens.  These do occupy a "no man's land" of taxonomic uncertainty (although there are many who claim to be certain enough) because lichens are entities that develop as a symbiosis between free-living taxa, a fungus (the mycobiont) and an alga (the phycobiont).  Current convention places the lichens within the Kingdom Fungi, and classifies them according to the species of the mycobiont (mostly ascomycetous fungi).  Click on the Amanita for images of the Kingdom Fungi.  (The Domain Eukarya Page)

Concepts and Terms

Click on the Subkingdom Taxa below for a more complete taxonomy (to the ordinal level) of the Kingdom Fungi.

REFERENCES.

This page written and maintained by Jack R. Holt & Carlos A. Iudica.  Last modified: 04/22/08