A molecular and morphological re-examination of the generic limits of truffles in the tarzetta-geopyxis lineage - Densocarapa, Hydnocystis and Paurocotylis

Truffle species within the /tarzetta-geopyxis lineage share smooth, globose, hyaline spores, but differ in the amount of convolution of hymenia in ascomata. The relation- ships among truffle species in this lineage have historically been confused. Phylogenetic analyses of the ITS and 28S nuclear ribosomal DNA from recently collected members of the /tarzetta-geopyxis lineage from Asia, Austral Asia, North America, and South America prompted a reinvestigation of species and generic limits in the truffle genera Hydnocystis, Paurocotylis, and Stephensia. Our analyses support emendations of Hydnocystis and Pauro- cotylis, abandonment of Stephensia and the resurrection of the genus Densocarpa. Nomen- clatural changes include the transfer of Stephensia bombycina to Hydnocystis, the transfer of Hydnocystis singeri and Stephensia bynumii to Paurocotylis, the reinstatement of Denso- carpa for Stephensia shanori and transfer of Stephensia crocea to Densocarpa. This is the first detection of the genus Paurocotylis in the Americas. We describe three new species, Hyd- nocystis transitoria from North America, Paurocotylis patagonica from South America, andPaurocotylis watlingii from Australia. Our work highlights the unexplored diversity, mor- phological plasticity, and remaining taxonomic problems among truffles in the /tarzetta- geopyxis lineage.