The boletoid genera
Butyriboletus and
Exsudoporus have recently been suggested by some researchers to constitute a single genus, and
Exsudoporus was merged into
Butyriboletus as a later synonym. However, no convincing arguments have yet provided significant evidence for this congeneric placement. In this study, we analyze material from
Exsudoporus species and closely related taxa to assess taxonomic and phylogenetic boundaries between these genera and to clarify species delimitation within
Exsudoporus. Outcomes from a multilocus phylogenetic analysis (ITS, nrLSU,
tef1-α and
rpb2) clearly resolve
Exsudoporus as a monophyletic, homogenous and independent genus that is sister to
Butyriboletus. An accurate morphological description, comprehensive sampling, type studies, line drawings and a historical overview on the nomenclatural issues of the type species
E. permagnificus are provided. Furthermore, this species is documented for the first time from Israel in association with
Quercus calliprinos. The previously described North American species
Exsudoporus frostii and
E. floridanus are molecularly confirmed as representatives of
Exsudoporus, and
E. floridanus is epitypified. The eastern Asian species
Leccinum rubrum is assigned here to
Exsudoporus based on molecular evidence, and a new combination is proposed. Sequence data from the original material of the Japanese
Boletus kermesinus were generated, and its conspecificity with
L. rubrum is inferred as formerly presumed based on morphology. Four additional cryptic species from North and Central America previously misdetermined as either
B. frostii or
B. floridanus are phylogenetically placed but remain undescribed due to the paucity of available material.
Boletus weberi (syn.
B. pseudofrostii) and
Xerocomus cf.
mcrobbii cluster outside of
Exsudoporus and are herein assigned to the recently described genus
Amoenoboletus. Biogeographic distribution patterns are elucidated, and a dichotomous key to all known species of
Exsudoporus worldwide is presented.
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