Hymenogaster macmurphyi and Splanchnomyces behrii are sequestrate species of Xerocomellus from the western United States

ABSTRACT

Hymenogaster is an ectomycorrhizal genus of brown-spored sequestrate fungi that is related to the mushroom-forming genera Hebeloma and Alnicola (Agaricales). However, because of difficulties in morphological taxonomy of sequestrate fungi, Hymenogaster has become a polyphyletic repository for a variety of unrelated brown-spored sequestrate species. During studies of ectomycorrhizal ecology and sequestrate fungal evolution in the western USA, we encountered specimens of a morphologically unique species. It was originally described as Hymenogaster macmurphyi, but our morphological and molecular analyses indicate that it is not closely related to Hymenogaster. Phylogenetic analyses of multiple gene regions indicate that H. macmurphyi is actually a member of the Boletineae (Boletales, Basidiomycota) and is nested within the epigeous genus Xerocomellus, distantly related to any of the other known genera of sequestrate Boletales. While examining additional herbarium collections, we came upon isotype material of Splanchnomyces behrii, which represents a closely related species. Here we document the morphology and phylogenetic affinities of these unusual sequestrate Boletineae and transfer both species to Xerocomellus as X. macmurphyi and X. behrii. During our study, we also noted that the sequestrate taxon Rhopalogaster transversarius is nested within the epigeous genus Suillus.

KEYWORDS:

• Boletales
• ectomycorrhizal
• Rhopalogaster
• sequestrate
• Splanchnomyces
• 2 new taxa

ACKNOWLEDGMENTS

We thank Dr. D. E. Desjardin of the Harry D. Thiers herbarium at San Francisco State University for access to field notes, color photographic slides, and collections of the late Mr. Herb Saylor, esteemed collector of sequestrate fungi in northern California. We added Mr. Saylor’s name as an authority for Xerocomellus macmurphyi for his early recognition that it was aberrant in Hymenogaster. Review of earlier versions of the manuscript was provided by Drs. Greg Bonito, Daniel Luoma, Darlene Southworth, and Kentaro Hosaka.

Additional information

Funding

Funding for M. E. Smith was provided by the National Institute of Food and Agriculture, US Department of Agriculture (award number FLA-PLP-005289), the University of Florida’s Institute for Food and Agricultural Sciences (IFAS), and Harvard University’s Farlow Postdoctoral Fellowship.