Three new species ofPythium: P. ershadii, P. pyrioosporum, and P. urmianumfrom soils of various regions in Iran are described and illustrated. These species are morphologically distinct from all other known species. Pythium ershadii is morphologically characterized by pyriform ornamented oogonia and rarely production of pyriform oospores.Pythium pyrioos-porumdiffers from other species of the genus by the production of pyriform oospores and smooth walled oogonia, oospores with a tapering elongation toward a hypogynous antheridium and intercalary hypogy-nous antheridia.Pythium urmianumis distinguished by the presence of intercalary hypogynous antheridia, smooth walled oogonia formed laterally on hyphae or on short side branches and peanut-shaped oospores. Phylogenetic relationships of these new taxa with other Pythiumspecies were investigated using internal tran-scribed spacers rDNA and partial coxI sequence data. The three species reside in clade E1 and are separated from closely related species
