Phytophthora parsiana has been considered as a unique and important pathogen in Iranian pistachio orchards, so far. The dawn of novel and closely related species to this evolutionary taxon in Clade 9 of Phytophthora spp. phylogenetic trees, including P. hydropathica, P. hydrogena and P. virginiana, as well as extremely heterogeneous morphological, physiologic and host rang of the assigned isolates, necessitates a comparative study of the isolates as a complex species. For this purpose, isolates that have been considered under this taxon during the last 25 years, along with the isolates which have been isolated in 2014- 2015 were studied. Single-strand-conformation polymorphism (SSCP) of ribosomal DNA was applied. The results of the patterns showed that the isolates assigned to P. parsiana were classified into four distinct groups in the Phytophthora spp. Clade 9 in comparison with other closely related species. The first group exclusively consisted of isolates obtained from pistachio orchards in Kerman and Yazd Provinces, which were alternately isolated between 2008 and 2014. The second group consisted of only two pistachio isolates from Kerman Province that were isolated only in 1993. The third group, containing single isolate of this taxon, created a completely separate group with completely distinct electrophoresis patterns on the polyacrylamide gel. This isolate has been reported only in 1991 from the root of fig tree with crown and root rot symptoms in Shabankareh region of Bushehr Province in Iran. The fourth group included isolates from Iranian and American pistachio plantations, which were reported in Iran in 2008 and 2014. The evidence from this grouping confirms the existence of a significant intra-species variation as well as the need for an overview of the initial description of this complex species. Molecular identification using nuclear and mitochondrial genes of identified groups, is under investigation.