A molecular and morphological analysis of the genus Rhizopogon subgenus Villosuli section Villosuli as a preface to ecological monitoring

Abstract

Rhizopogon (Boletales) represents a model genus for ecological studies of ectomycorrhizal fungi, but the identification of species in subgenus Villosuli section Villosuli has long been challenging due to variation in taxonomically informative morphological characters. Here we re-examine species concepts in this section using data from nuclear ribosomal internal transcribed spacer (ITS) and large subunit (LSU) sequences as well as spore measurements. Our phylogenetic analyses from 34 type and non-type collections of eight species, including the seven currently recognized in this section, found consistent support for only three species-level clades. Each of the clades had a significantly different combination of mean spore widths and Q ratios using digital-assisted measurements, which suggests both molecular and spore-based morphological approaches can be used to identify species in this section. Based on our analysis, we propose that only three species names be applied to future ecological studies: R. hawkerae, R. parksii and R. villosulus. We consider R. subareolatus and R. colossus as taxonomic synonyms of R. hawkerae and R. pseudovillosulus, R. rogersii, R. villescens and R. zelleri as taxonomic synonyms of R. villosulus.

• ecology
• ITS
• LSU
• Rhizopogon
• spore size
• taxonomy
• Villosuli

Acknowledgments

We thank Tim James and Patricia Rogers of the University of Michigan Herbarium, Joey Spatafora and Alija Mujic of the OSC herbarium at Oregon State University and Mike Castellano of the U.S.F.S. for providing collections; Alija Mujic and Jim Trappe for providing many helpful discussions about the genus Rhizopogon and the OSC herbarium record data (Supplementary fig. 3); Logan Higgins for helping with DNA extraction and amplification; Else Vellinga, Matt Trappe, Alija Mujic and two anonymous reviewers for their comments on drafts of this manuscript. Financial support was provided by the National Science Foundation (grant DEB 1020735 to PGK).