Abstract
Acremonium is a cosmopolitan and diverse genus of filamentous fungi, commonly isolated from soil and plant material, with several species recognized as opportunistic pathogens in both plants and humans. In this study, a novel species, Acremonium quercivorum sp. nov., is described from declining oak (Quercus spp.) trees in Algeria. This species is characterized by thin-walled hyphae, conidia oblong-ellipsoidal, and rounded at the apex, and subulate phialides with a thin neck at the apex. The multi-locus phylogenetic analyses combining ITS, LSU, RPB2, and TEF1 sequence data provide robust evidence supporting its distinction from A. egyptiacum and other closely related taxa. Comprehensive morphological descriptions, micrographs, and phylogenetic analyses of the new taxon associated with oak dieback are presented.