The most dramatic shifts in the classification relative to previous works concern the groups that have traditionally been included in the Chytridiomycota and Zygomycota. The Chytridiomycota is retained in a restricted sense, with Blastocladiomycota and Neocallimastigomycota representing segregate phyla of flagellated Fungi. Taxa traditionally placed in Zygomycota are distributed among Glomeromycota and several subphyla incertae sedis, including Mucoromycotina, Entomophthoromycotina, Kickxellomycotina, and Zoopagomycotina. Microsporidia are included in the Fungi, but no further subdivision of the group is proposed. Several genera of 'basal' Fungi of uncertain position are not placed in any higher taxa, including Basidiobolus, Caulochytrium, Olpidium, and Rozella.

Inconspicuous basidiomycetes from the order Sebacinales are known to be involved in a puzzling variety of mutualistic plant-fungal symbioses (mycorrhizae), which presumably involve transport of mineral nutrients. Recently a few members of this fungal order not fitting this definition and commonly referred to as ‘endophytes’ have raised considerable interest by their ability to enhance plant growth and to increase resistance of their host plants against abiotic stress factors and fungal pathogens. Using DNA-based detection and electron microscopy, we show that Sebacinales are not only extremely versatile in their mycorrhizal associations, but are also almost universally present as symptomless endophytes. They occurred in field specimens of bryophytes, pteridophytes and all families of herbaceous angiosperms we investigated, including liverworts, wheat, maize, and the non-mycorrhizal model plant Arabidopsis thaliana. They were present in all habitats we studied on four continents. We even detected these fungi in herbarium specimens originating from pioneering field trips to North Africa in the 1830s/40s. No geographical or host patterns were detected. Our data suggest that the multitude of mycorrhizal interactions in Sebacinales may have arisen from an ancestral endophytic habit by specialization. Considering their proven beneficial influence on plant growth and their ubiquity, endophytic Sebacinales may be a previously unrecognized universal hidden force in plant ecosystems.

The simple-septate basidiomycetes comprise more than 8,000 species that show a high morphological and ecological heterogeneity. To gain insight in the phylogenetic relationships within this group, we compared several ultrastructural features such as septal pore apparatus, form and behavior of the spindle pole bodies, types of host-parasite interaction, presence or absence of colacosomes, symplechosomes, atractosomes and cystosomes as well as nuclear rDNA sequences coding for small-and large-subunit rRNA. Based on our integrated analysis, we propose a new classification system for the simple-septate basidiomycetes with the subphylum Pucciniomycotina and the

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Summary• Heterobasidiomycetous species of the Sebacinaceae family, previously considered as saprophytes or parasites, are shown here to form ectomycorrhizas on temperate forest trees.• Ectomycorrhizas were collected under sebacinoid sporophores and near root systems of Neottia nidus-avis, an orchid symbiotic with sebacinoids. To identify the partners each ectomycorrhiza was submitted to amplification and sequencing of the plant and fungal internal transcribed spacer (ITS), and further investigated by light and electron microscopy whenever a sebacinoid ITS was found.• Molecular and microscopic analyses correlated well. Two sebacinoids of divergent rDNA sequences were demonstrated to form similar ectomycorrhizas, with a welldeveloped Hartig net and a hyphal mantle having thick-walled outer mantle hyphae. The ultrastructure of the septal pore (dolipore with imperforate caps) was typical for sebacinoids. In one case, intracellular colonization was seen. The ectomycorrhizal host range of these sebacinoids was not specific and included Betulaceae, Fagaceae and Tiliaceae.• Sebacinoids probably represent an overlooked ectomycorrhizal group and ectomycorrhizal symbiosis may be common among basal lineages of hymenomycetes.

To identify monophyletic groups within the smut fungi and related taxa, characteristics of hyphal septation and zones of host–parasite interaction were analyzed by serial-section electron microscopy of 139 species belonging to 50 smut and 10 allied genera. Our results support the hypothesis of the existence of two phylogenetically separate lines of smut fungi. The first line, the Microbotryales, is composed of Aurantiosporium, Fulvisporium, Liroa, Microbotryum, Sphacelotheca, and Ustilentyloma, which are distributed into the Ustilentylomataceae and Microbotryaceae. The second monophyletic line, the Ustilaginomycetes, is formed by the remaining smut fungi studied here together with the Exobasidiales, Graphiolales, and Cryptobasidiales (in the traditional sense). The ultrastructural analysis identifies three lineages within the Ustilaginomycetes. The Entorrhizomycetidae are represented by Entorrhiza. The Ustilaginomycetidae consist of the Urocystales and Ustilaginales. The Exobasidiomycetidae are composed of the Doassansiales, Entylomatales, Exobasidiales, Georgefischeriales, Graphiolales, Microstromatales, and Tilletiales. The Entorrhizomycetidae, Exobasidianae, Entorrhizales, Entylomatales, Doassansiales, Georgefischeriales, Microbotryales, Microstromatales, Tilletiales, Urocystales, Entorrhizaceae, Entylomataceae, Georgefischeriaceae, Mycosyringaceae, Rhamphosporaceae, and Ustilentylomataceae are proposed as new taxa. The descriptions of the Exobasidiomycetidae, Ustilaginomycetidae, Exobasidiales, Ustilaginales, Doassansiaceae, Tilletiaceae, and Ustilaginaceae are emended. Some species of Ustilago are transferred to Microbotryum. Key words: basidiomycetes, classification, Exobasidiales, Graphiolales, phylogeny, smut fungi, ultrastructure.

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.

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