Clarifying species boundaries in oak powdery mildews: description of Erysiphe quercus-palustris sp. nov. and notes on E. abbreviata

Abstract Powdery mildews ( Erysiphaceae ) are obligate fungal pathogens that infect over 10,000 plant taxa worldwide. Oaks ( Quercus spp.) are a particularly important group of hosts due to their ecological and economic value. Recent molecular work has revealed that species infecting North American oaks are more diverse and host-specific than previously recognized. Here, we describe Erysiphe quercus-palustris sp. nov., collected on Quercus palustris in North Carolina, and clarify the placement of the previously described species E. abbreviata . Phylogenetic analyses support the separation of the new species from the main “North American” Erysiphe clade whose species are typically characterized by aerial hyphae, a feature absent in E. quercus-palustris . This study contributes to the growing evidence of cryptic diversity within oak-infecting powdery mildews and underscores the importance of continued taxonomic and phylogenetic research on pathogens of ecologically important hosts.