Background: Section Calochroi is one of the most species-rich lineages in the genus Cortinarius (Agaricales, Basidiomycota) and is widely distributed across boreo-nemoral areas, with some extensions into meridional zones. Previous phylogenetic studies of Calochroi (incl. section Fulvi) have been geographically restricted; therefore, phylogenetic and biogeographic relationships within this lineage at a global scale have been largely unknown. In this study, we obtained DNA sequences from a nearly complete taxon sampling of known species from Europe, Central America and North America. We inferred intra-and interspecific phylogenetic relationships as well as major morphological evolutionary trends within section Calochroi based on 576 ITS sequences, 230 ITS + 5.8S + D1/D2 sequences, and a combined dataset of ITS + 5.8S + D1/D2 and RPB1 sequences of a representative subsampling of 58 species.

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.

Phylogenetic relationships in the genus Cortinarius with emphasis on European species were studied by integrating a molecular phylogenetic analysis of nuclear rDNA sequences with morphological, chemical, and ecological data. Internal transcribed spacers (ITS1 and ITS2, including 5.8S) and the D1–D2 regions of nuclear rDNA of 262 Cortinarius species including most of the recognised subgenera from Europe, South America, Australia, Tasmania, New Zealand, and Asia were sequenced and analysed by maximum likelihood and neighbour joining. Our morphological and molecular analyses showed considerable disagreement with earlier morphology-based hypotheses concerning the infrageneric delimitations in Cortinarius. We propose a new base for a more natural classification system in Cortinarius involving the taxonomic rearrangement of the species into the following major lineages that we informally designate as “clades” at this time: (1) phlegmacioid species are included in Alluti, Amarescentes, Arguti, Calochroi, Caerulescentes, Percomes, Phlegmacioides, Phlegmacium, Purpurascentes, Scauri, and Vulpini; (2) the Heterocliti clade includes species of the subgenera Leprocybe and Cystogenes ; (3) most of the Myxacium species are included in the Delibuti and Myxacium clades; (4) part of Rozites are included in the Rozites clade; (5) the north-hemispheric species of subgenus Dermocybe are included in the Dermocybe clade and part of the south-hemispheric species in the Splendidi clade; (6) part of Sericeocybe are integrated in the Anomali and Telamonia clades; (7) members of subgenus Cortinarius are assigned to the Cortinarius clade; (8) telamonioid taxa are included in the Obtusi, Renidentes, and Telamonia clades. Several Cortinarius species with peculiar patterns of morphology and basidiome coloration had isolated positions in the sequence analysis, and the evolutionary relationships among the major lineages remained unresolved. Our results suggest the convergent evolution of certain morphological traits across phylogenetically divergent lineages in Cortinarius. However, combinations of features such as pileipellis anatomy, spore shape, veil coloration, basidiome pigments, and stipe shape appear useful to circumscribe clades. Our molecular phylogenetic analysis allows insights in global geographical patterns of species distribution within the major lineages in the genus Cortinarius. The clade structure proposed here could be used as backbone for further more detailed systematic studies.

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