SummaryA reverse taxonomic approach for characterisation of several populations of an aphelenchid nematode recovered from declined oak trees in the Zagros forests, Ilam, western Iran, revealed that their 28S rDNA D2-D3 sequences matched two available sequences of the same genomic fragment belonging to two species,Laimaphelenchus belgradiensisandL. hyrcanus. Further morphological studies yielded new morphological traits that had been overlooked in their original descriptions, and a new hypothesis helping to disentangle these taxa, which have the same 28S sequences and the same phylogenetic placement, is proposed. In a similar fashion, the taxonomic status of some other species of the genus having a similar morphology or similar genomic sequences are reviewed. The possibility of proposing new synonyms was evaluated and tentative reasons for the new habitat of the recovered populations ofLaimaphelenchusfrom the Zagros forests discussed.