Rhizopogon subgenus Villosuli are the only members of the genus known to form an ectomycorrhizal relationship exclusively with Pseudotsuga. The specificity of this host relationship is unusual in that Rhizopogon is broadly associated with several tree genera within the Pinaceae and relationships with a host genus are typically distributed across Rhizopogon subgenera. Naturally occurring specimens of R. subg. Villosuli have been described only from North American collections, and the unique host relationship with Pseudotsuga is demonstrated only for Rhizopogon associated with P. menziesii (Douglas-fir), the dominant species of Pseudotsuga in North America. Species of Pseudotsuga are naturally distributed around the northern Pacific Rim, and Rhizopogon associates of other Pseudotsuga spp. are not yet described. Here we present the results of field sampling conducted in P. japonica forests throughout the Japanese archipelago and describe Rhizopogon togasawariana sp. nov., which occurs in ectomycorrhizal association with P. japonica. Placement of this new species within R. subg. Villosuli is supported by morphological and molecular phylogenetic analysis, and its implications to Pseudotsuga-Rhizopogon biogeography are discussed.
Keywords: Japan; Rhizopogon subgenus Villosuli; biogeography; ectomycorrhizae; hypogeous; truffle.