Ectomycorrhizal iconoclasts: the ITS rDNA diversity and nitrophilic tendencies of fetid Russula

Fetid Russula are frequently dominant ectomycorrhizal fungi, and some appear to be especially nitrophilic. However, little is known about their phylogenetic relationships or how common nitrophilic traits are in this group. This study addresses this gap and presents a phylogenetic analysis of ITS rDNA sequences and a meta-analysis of studies that examine ectomycorrhizal fungi response to nitrogen increase. The phylogenetic analysis indicates that (i) this lineage contains numerous unidentified taxa; (ii) the taxa have distinct geographic distributions; and (iii) the misuse of names such as R amoenolens, R. foetens or R. pectinatoides is common. Twenty-three well supported phylotypes were identified and include clades specific to western North America, eastern North America, Europe and Asia, while morphologically similar collections from tropical-equatorial regions are distinct. The metaanalysis shows that nitrophilic tendencies appear throughout fetid Russulas suggesting that this character is not an isolated trait within this subgenus but instead is a more general feature of the group overall. Mapping these tendencies across a broader portion of the Russulaceae shows that this trait is more regularly found in the basal Russula lineages and Lactarius spp., suggesting that this ability evolved early in these fungi.