Resolving taxonomic and phylogenetic incongruence within species Ceratocystiopsis minuta

Ceratocystiopsis minuta (Siemaszko) H.P. Upadhyay & W.B. Kendr., originally isolated in Poland, is the type species of genus Ceratocystiopsis H.P. Upadhyay & W.B. Kendr. Species in this genus are characterized by dark perithecia with short conical beaks, usually with convergent ostiolar hyphae and dark ascocarps, and by falcate or lunate ascospores. Work within the genus is complicated by historical inconsistencies, errors in strain identification and the absence of a holotype specimen. We used sequence data from the beta-tubulin gene, internal transcribed spacer and large subunit regions of ribosomal DNA to phylogenetically characterize 23 putative strains of Cop. minuta from Europe, Japan and North America, as well as strains from other species in genus Ceratocystiopsis. Our results show that Cop. minuta strains from Europe and Japan are monophyletic, whereas those from North American are polyphyletic and likely misidentified. This suggests that prior research groups have used misidentified strains of Cop. minuta or fungal strains that were only distantly related to the Cop. minuta strain originally described from Poland. Further our multigene phylogenetic analysis also shows that Cop. minuta strains from Europe and Japan can be segregated into three clades. This suggests the presence of several phylogenetic species that are morphologically similar to Cop. minuta, and we anticipate that this species complex will challenge researchers until such relationships are resolved.