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

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 digitalassisted 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.