Downfall of an empire: Unmasking the hidden diversity and distribution of the species complex.

is one of the most salient mushroom genera due to its cultural, economic, and medical importance. Recently, many new species have been described worldwide, increasing the genus richness. However, several clades have cryptic diversity, and many species complexes have not yet been resolved. This is the case of the rubescent species in the section, which have been widely cited under the name s.l. We used a four-locus matrix (nuc rDNA internal transcribed spacer [ITS] and 28S regions and genes for RNA polymerase II subunit 2 [], translation elongation factor 1-α [], and β-tubulin []) to solve the phylogenetic relationships within the section . To analyze the diversity and distribution patterns of species, we used an extensive ITS sequence sampling including environmental DNA databases. The phylogenetic analyses demonstrated that the section is divided into three monophyletic and highly supported major clades: , and . At least 11 species-level clades within the clade were highly supported: nom. prov. s.s. (European clade), s.s. (Asiatic clade), s.s. . ',' nom. prov., , and two undescribed North American species. We proved that s.s. has two segregated populations (European and Asiatic) and it is not naturally distributed in America. Furthermore, we found that America has more cryptic species within the clade than Eurasia.