Classification
Biological classification is a system used to group and characterize taxa into different groups within the taxonomic hierarchy. Modern biological classification has its origins in the works of Carolus Linneaus who grouped species according to their physical characteristics and proposed the binomial system of biological nomenclature. Biological classifications should be based on shared characters from a common ancestor and constructed by analyzing homologous characters. Classification should not be confused with taxonomy, which refers to finding, describing and naming taxa of living or fossil species (alpha taxonomy).
Classification and taxonomy of arbuscular mycorrhizal fungi (AMF) were based until the end of the 20th century on the morphological analysis of the spore wall differentiated by these fungi (phenotypic characters). At the dawn of the present century, genetic characters were used to propose new classifications and new taxa and, as a consequence, the classification and taxonomy of AMF has experienced a period of intense discussion and changes.
Stürmer (2012) recognizes four periods in the history of taxonomy and systematics of AMF:
1) The Discovery Period (1845-1974)
2) The Alpha Taxonomy Period (1975-1989)
3) The Cladistic Period (1990-2000)
4) The Phylogenetic Synthesis Period (2001 up to now)
Six classification proposals for AMF have been presented since the classic work of Gerdemann & Trappe (1974) and they are presented and discussed below.
3) Schüssler, Schwarzott & Walker (2001)
5) Oehl, Sieverding, Palenzuela, Ineichen, da Silva (2011)
6) Redecker, Schüssler, Stockinger, Stürmer, Morton & Walker (2013)