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The butter boletes (Boletus s.l. sect. Appendiculati) are an economically important group of ectomycorrhizal fungi whose basidiocarps have a yellow tube layer that often bruises blue, yellow reticulate stipe, mild flavor and firm yellow-tinged flesh that may or may not turn blue when exposed. Morphological characters and molecular data (ITS and LSU) place this group in a separate phylogenetic clade from Boletus sensu stricto. Here we establish a new genus, Butyriboletus, to accommodate 14 species of butter boletes that range from Asia to Europe, north Africa and North America. We recombine eight previously described butter bolete species and we describe six new species: four from western USA (Bu. persolidus, Bu. primiregius, Bu. autumnigius, Bu. querciregius) and two from Yunnan, China (Bu. yicibus, Bu. sanicibus).
Acknowledgments
We are extremely grateful for the help of those who provided voucher collections for our study: John Banks, Michael Beug, Dimitar Bojantchev, Herman Brown, Matteo Gelardi, Jeanne Jackson, Nicholas Janson, Louis Jeandin, Freddie Menge, Alija Mujic, Pavel Nedelev, Jay Scelza, Noah Siegel, Hugh Smith, Wendy So, Andy Taylor, Dave Wasilewski, and Zhu Gui Feng. We thank Dr Dennis Desjardin of San Francisco State University and Dr Joey Spatafora of Oregon State University for facilitating our study of herbarium collections and Dr Wang Xianghua of the Kunming Institute of Botany for her assistance there. Dr Shaun Pennycook provided valuable nomenclatural guidance. We thank Dr David Oline of Southern Oregon University for helpful discussions regarding phylogenetic analyses, Dr James Trappe for his assistance in helping to choose Latin names, and Dimitar Bojantchev, Dr Tom Bruns, and Dr Matthew Smith for making valuable suggestions and for reviewing the manuscript before publication.