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Abstract
The genus Suillus represents one of the most recognizable groups of mushrooms in conifer forests throughout the Northern Hemisphere. Although for decades the genus has been relatively well defined morphologically, previous molecular phylogenetic assessments have provided important yet preliminary insights into its evolutionary history. We present the first large-scale phylogenetic study of the boundaries of each species in the genus Suillus based on the most current internal transcribed spacer (ITS) barcode sequences available inPUBLIC databases, as well as sequencing of 224 vouchered specimens and cultures, 15 of which were type specimens from North America. We found that species boundaries delimited by morphological data are broadly congruent with those based on ITS sequences. However, some species appear to have been described several times under different names, several species groups cannot be resolved by ITS sequences alone, and undescribed taxa are apparent, especially in Asia. Therefore, we elevated S. tomentosus var. discolor to S. discolor; proposed synonymies of S. neoalbidipes with S. glandulosipes, S. borealis with S. brunnescens, Boletus serotinus and B. solidipes with Suillus elbensis, S. lactifluus with S. granulatus, S. himalayensis with S. americanus; and proposed usage of the names S. clintonianus in the place of the North American S. grevillei, S. weaverae for North American S. granulatus, S. ampliporus in the place of the North American S. cavipes, and S. elbensis in place of the North American S. viscidus. We showed that the majority of Suillus species have strong affinities for particular host genera. Although deep node support was low, geographic differentiation was apparent, with species from North America, Eurasia, and Asia often forming their own clades. Collectively, this comprehensive genus-level phylogenetic integration of currently available Suillus ITS molecular data and metadata will aid future taxonomic and ecological work on an important group of ectomycorrhizal fungi.
Acknowledgments
This work is a culmination of that which the first author (NHN) started 10 y ago. He thanks Tom Bruns for putting the genus on his radar when he first joined his lab as a graduate student, for the continuing support and excitement for anything in the genus, and for having never tossed a maggot-ridden Suillus at him. He thanks Else Vellinga for the many years of educating him about mushroom taxonomy and stimulating times annotating the working Suillus tree, and Peter Kennedy for the unyielding support and excitement about Suillus. The work could not have been accomplished without the type and important specimens that were loaned by MICH, DBG, and SFSU. We thank Todd Osmundson and Valerie Wong for the Perl script that gathers metadata from GenBank sequences. Special and continuing thanks to the Colorado mycology group: Vera Evenson (DBG) and the Colorado Mycological Society, along with Brian Barzee and the Pike’s Peak Mycological Society, contributed significant numbers of specimens from Colorado to this project. Brian Barzee hosted and field-guided two successful collecting forays to study Suillus in Colorado, and sequences of specimens from those forays can be found in this study. Sara Branco, Noah Siegel, Beatrice Senn-Irlet, Matthew Smith, Roy Halling, Debbie Viess, David Rust, Ernst Both, Walt Sturgeon, Michael Kuo, and Donna Mitchell, in addition to the many others who have contributed specimens to this study. Some specimens were sequenced by undergraduates Lisa Rosenthal and Blake Boeing. Beatriz Ortiz-Santana provided sequences from the Dominican Republic and Belize, among other locations; Sara Branco, Rytas Vigalys, and Lotus Lofgren provided some sequences of respective regional specimens. This study was partially funded by NSF GRFP to NHN and DEB 1554181 to Rytas Vigalys and PGK.