Phylogeny and origin of 82 zygomycetes from all 54 genera of the Mucoralesand Mortierellales based on combined analysis of actin and translation elongation factor EF-1 alpha genes

True fungi (Eumycota) are heterotrophic eukaryotic microorganisms encompass ing ascomycetes, basidiomycetes, chytridiomycetes and zygomycetes. The natu ral systematics of the latter group, Zygomycota, are very poorly understood due to the lack of distinguishing morphological characters. We have determ ined sequences for the nuclear-encoded genes actin (act) from 82 zygomycete s representing all 54 currently recognized genera from the two zygomycetous orders Mucorales and Mortierellales. We also determined sequences for tran slation elongation factor EF-1 alpha (tef) from 16 zygomycetes (total of 96 ,837 bp). Phylogenetic analysis in the context of available sequence data ( total 2,062 nucleotide positions per species) revealed that current classif ication schemes for the mucoralean fungi are highly unnatural at the family and, to a large extent, at the genus level. The data clearly indicate a de ep. ancient and distinct dichotomy of the orders Mucorales and Mortierellal es, which are recognized only in some zygomycete systems. Yet at the same t ime the data show that two genera Umbelopsis and Micromucor - previously pl aced within the Mortierellales on the basis of their weakly developed colum ella (a morphological structure of the sporangiophore well-developed within all Mucorales) are in fact members of the Mucorales. Phylogenetic analyses of the encoded amino acid sequences in the context of homologues from euka ryotes and archaebacterial outgroups indicate that the Eumycota studied her e are a natural group but provide little or no support for the monophyly of either zygomycetes, ascomycetes or basidiomycetes. The data clearly indica te that a complete revision of zygomycete natural systematics is necessary. (C) 2001 Elsevier Science B.V. All rights reserved.