The <i>Cedrus</i>-associated truffle <i>Trappeindia himalayensis</i> is a morphologically unique and phylogenetically divergent species of <i>Rhizopogon</i>

In the northwestern Himalayan mountains of India, the hypogeous sequestrate fungus <i>Trappeindia himalayensis</i> is harvested from forests dominated by the ectomycorrhizal tree <i>Cedrus deodara</i> (Himalayan cedar). This truffle has basidiospores that are ornamented with raised reticulation. The original description of <i>Trappeindia himalayensis</i> suggested that the gleba of this species is similar to young specimens of <i>Scleroderma</i> (Boletales), whereas its basidiospores are ornamented with raised reticulation, suggesting a morphological affinity to <i>Leucogaster</i> (Russulales) or <i>Strobilomyces</i> (Boletales). Given this systematic ambiguity, we have generated DNA sequence data from type material and other herbarium specimens and present the first molecular phylogenetic analysis of this unusual <i>Cedrus</i>-associated truffle. Despite the irregular ornamented basidiospore morphology, <i>T. himalayensis</i> is resolved within the genus <i>Rhizopogon</i> (Suillineae, Boletales) and represents a unique lineage that has not been previously detected. All known <i>Rhizopogon</i> species possess an ectomycorrhizal trophic mode, and because of its placement in this lineage, it is likely that <i>Trappeindia himalayensis</i> is an ectomycorrhizal partner of <i>Cedrus deodara</i>. This study highlights the importance of generating sequence data from herbarium specimens in order to identify fungal biodiversity and clarify the systematic relationships of poorly documented fungi.