A phylogenetic hypothesis of Ustilaginomycotina based on multiple gene analyses and morphological data.

The subphylum Ustilaginomycotina comprises about 1500 species of basidiomycetous plant parasites. They are usually dimorphic, producing a saprobic haploid yeast phase and a parasitic dikaryotic hyphal phase. With only a few exceptions they occur on angiosperms and are found mainly on members of the Poaceae and Cyperaceae. Molecular methods recently have shown that anamorphic species such as members of Malassezia or Tilletiopsis should be included in this group. Here we present the most recent consensus as to the phylogeny of this group and discuss its relevant characteristics. Our morphological, ultrastructural and molecular phylogenetic data point to the existence of three lines of Ustilaginomycotina: Entorrhizomycetes, Ustilaginomycetes and Exobasidiomycetes. Entorrhizomycetes is represented by Entorrhizales, a small group of unusual teliosporic root parasites on Juncaceae and Cyperaceae. Ustilaginomycetes, to which the majority of Ustilaginomycotina belong, is a teliosporic and gastroid group characterized by the presence of enlarged interaction zones. Ustilaginomycetes is dichotomous, consisting of predominantly holobasidiate Urocystales and predominantly phragmobasidiate Ustilaginales. Exobasidiomycetes forms local interaction zones. This group is predominantly holobasidiate and consists of teliosporic Doassansiales, Entylomatales, Georgefischeriales and Tilletiales, nonteliosporic Ceraceosorales, Exobasidiales and Microstromatales, as well as the anamorphic Malasseziales. Entorrhizomycetes, Exobasidiomycetes and Ceraceosorales are proposed as new taxa, and the description of Ustilaginomycetes is emended.