Choosing one name for pleomorphic fungi: The example of Aspergillus versus Eurotium, Neosartorya and Emericella

摘要

With the termination of dual nomenclature, each fungus may have only one name. Now mycologists must choose between genus names formerly applied to taxa with either asexual or sexual reproductive modes, a choice that often influences the breadth of genotypic and phenotypic diversity in a genus, and even its monophyly. We use the asexual genus Aspergillus to examine the problems involved in such choices because (a) 11 sexual generic names are associated with it and (b) phenotypic variation and genetic divergence within sexual genera are low but between sexual genera are high. As a result, in the case of Aspergillus, applying the asexual name to the many sexual genera masks information now conveyed by the genus names and would lead to taxonomic inconsistency in the Eurotiales because this large Aspergillus would then embrace more genetic divergence than neighboring clades comprised of two or more genera. Two proposals have been published concerning this problem as it relates to Aspergillus: one advocates a broad concept, referred to here as "Wide Aspergillus", which embraces as many Aspergillus species as possible while maintaining Penicillium as a separate genus; the other, referred to here as "Narrow Aspergillus", preserves this genus for a much smaller group of closely related species and retains many of the sexual genera. Phylogenetic analyses detailed here show that, to be monophyletic, Wide Aspergillus must embrace several genera morphologically discordant with Aspergillus, including Penicillium, Phialosimplex and Polypaecilum. Likelihood ratio tests reject a Wide Aspergillus that excludes Phialosimplex and Polypaecilum. Phylogenetic Rank Boundary Optimization, which employs the genetic divergence measure, maximum subtree height, to assess inconsistency in the ranking of genera and species, shows that Narrow Aspergillus provides a more consistent taxonomy than Wide Aspergillus. Adopting Narrow Aspergillus and retaining sexual names instead of adopting Wide Aspergillus will result in genera that convey precise morphological and physiological information, that are monophyletic, and that are taxonomically consistent.