Endophytic Xenodidymella from Iranian medicinal plants: description of three novel species and a new host record

During a survey of endophytic fungi associated with medicinal plants in Iran, three novel species of the genus Xenodidymella including X. euphorbiae, X. hamanae and X. kopetdagensis were isolated from asymptomatic tissues of Euphorbia kopetdaghi Prokh and Thymus transcaspicus Klokov. Species delimitation was conducted using a combination of morphological characterisation and multilocus phylogenetic analyses based on the ITS rDNA, partial beta-tubulin (tub2), and RNA polymerase II second largest subunit (rpb2) gene regions. Both Bayesian inference and Maximum Likelihood phylogenetic analyses revealed that each new species formed distinct, well-supported clades, clearly separated from previously known taxa. In addition, Xenodidymella camporesii is reported for the first time from healthy roots of Salvia sclarea L., representing a novel host record. These findings suggest a potential endophytic lifestyle for Xenodidymella species, contrasting with their traditionally known roles as pathogens or saprobes. This study contributes to the taxonomic expansion of the genus and underscores the rich, yet underexplored fungal diversity of Iran's arid and semi-arid ecosystems.