Advancing the taxonomy of Sclerotinia (Helotiales, Sclerotiniaceae): a review and recommendations for an important plant-pathogenic genus

<i>Sclerotinia</i> is a fungal genus of significant agricultural and scientific importance, as it includes multiple plant pathogens and provides an informative case study for mechanisms of host generalism. However, the taxonomy of this group remains unsettled, which hinders research on these pathogens. The last monographic treatment of <i>Sclerotinia</i> was published more than 40 years ago and was centered on the morphological data available at that time. Here, we examine that revision alongside other pivotal publications to trace the taxonomic history of <i>Sclerotinia</i> and to evaluate the morphological traits used to identify <i>Sclerotinia</i> species. We also briefly assess the composition of genera in the family <i>Sclerotiniaceae</i>, emphasising the need for a modern taxonomic investigation of the broader group. Thirteen new <i>Sclerotinia</i> species have been described since the last taxonomic revision, including <i>Sclerotinia antarctica</i>, <i>S. asari</i>, <i>S. atrostipitata</i>, <i>S. cirsii-spinosissimi</i>, <i>S. ginseng</i>, <i>S. glacialis</i>, <i>S. himalayensis</i>, <i>S. nivalis</i>, <i>S. pseudoplatani</i>, <i>S. subarctica</i>, <i>S. tetraspora</i>, <i>S. trillii</i>, and <i>S. verrucispora</i>. These species are evaluated here. Finally, several recommendations are made regarding how future taxonomic research on <i>Sclerotinia</i> should incorporate molecular data. We highlight potential obstacles and opportunities for this research, including the limitations of the internal transcribed spacer rDNA region (ITS) as a DNA barcode and the untapped potential of genomic data for the genus. By outlining the gaps that need to be addressed, this review charts a course toward a clearer understanding of taxonomic relationships among <i>Sclerotinia</i> species. This understanding will facilitate research into other aspects, such as pathogenicity and host generalism, and may ultimately contribute to improved management of the devastating diseases caused by these pathogens.