Phylogeny of the Zygomycota Based on Nuclear Ribosomal Sequence Data

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The Zygomycota is an ecologically heterogenous assemblage of nonzoosporic fungi comprising two classes, Zygomycetes and Trichomycetes. Phylogenetic analyses have suggested that the phylum is polyphyletic; two of four orders of Trichomycetes are related to the Mesomycetozoa (protists) that diverged near the fungal/animal split. Current circumscription of the Zygomycota includes only orders with representatives that produce zygospores. We present a molecular-based phylogeny including recognized representatives of the Zygomycetes and Trichomycetes with a combined dataset for nuclear rRNA 18S (SSU), 5.8S and 28S (LSU) genes. Tree reconstruction by Bayesian analyses suggests the Zygomycota is paraphyletic. Although 12 clades were identified only some of these correspond to the nine orders of Zygomycota currently recognized. A large superordinal clade, comprising the Dimargaritales, Harpellales, Kickxellales and Zoopagales, grouping together many symbiotic fungi, also is identified in part by a unique septal structure. Although Harpellales and Kickxellales are not monophyletic, these lineages are distinct from the Mucorales, Endogonales and Mortierellales, which appear more closely related to the Ascomycota + Basidiomycota + Glomeromycota. The final major group, the insect-associated Entomophthorales, appears to be polyphyletic. In the present analyses Basidiobolus and Neozygites group within Zygomycota but not with the Entomophthorales. Clades are discussed with special reference to traditional classifications, mapping morphological characters and ecology, where possible, as a snapshot of our current phylogenetic perspective of the Zygomycota.