title: Species delimitation in taxonomically difficult fungi: the case of Hymenogaster.
abstract: BACKGROUND
  False truffles are ecologically important as mycorrhizal partners of trees and evolutionarily highly interesting as the result of a shift from epigeous mushroom-like to underground fruiting bodies. Since its first description by Vittadini in 1831, inappropriate species concepts in the highly diverse false truffle genus Hymenogaster has led to continued confusion, caused by a large variety of prevailing taxonomical opinions.
  
  
  METHODS
  In this study, we reconsidered the species delimitations in Hymenogaster based on a comprehensive collection of Central European taxa comprising more than 140 fruiting bodies from 20 years of field work. The ITS rDNA sequence dataset was subjected to phylogenetic analysis as well as clustering optimization using OPTSIL software.
  
  
  CONCLUSIONS
  Among distinct species concepts from the literature used to create reference partitions for clustering optimization, the broadest concept resulted in the highest agreement with the ITS data. Our results indicate a highly variable morphology of H. citrinus and H. griseus, most likely linked to environmental influences on the phenology (maturity, habitat, soil type and growing season). In particular, taxa described in the 19(th) century frequently appear as conspecific. Conversely, H. niveus appears as species complex comprising seven cryptic species with almost identical macro- and micromorphology. H. intermedius and H. huthii are described as novel species, each of which with a distinct morphology intermediate between two species complexes. A revised taxonomy for one of the most taxonomically difficult genera of Basidiomycetes is proposed, including an updated identification key. The (semi-)automated selection among species concepts used here is of importance for the revision of taxonomically problematic organism groups in general.
authors.affiliation: DSMZ-German Collection of Microorganisms and Cell Cultures, Braunschweig, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Stielow
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Bratek
authors.forename: Akos Kund I
authors.initials: AK
authors.lastname: Orczán
authors.forename: Szabolcs
authors.initials: S
authors.lastname: Rudnoy
authors.forename: Gunnar
authors.initials: G
authors.lastname: Hensel
authors.forename: Peter
authors.initials: P
authors.lastname: Hoffmann
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Klenk
authors.forename: Markus
authors.initials: M
authors.lastname: Göker
mesh_terms: D001483:Base Sequence; D001487:Basidiomycota / Q000145:classification* / Q000235:genetics; D002965:Classification; D016000:Cluster Analysis; D004275:DNA, Ribosomal / Q000235:genetics; D005060:Europe; D049810:Genetic Speciation; D010802:Phylogeny; D016415:Sequence Alignment
chemical_list: D004275:DNA, Ribosomal