SummaryAmong the recognised species groups ofHeterodera, theAvenaegroup is one of the largest with a total of 12 species. Ten of them,H. arenaria,H. aucklandica,H. australis,H. avenae,H. filipjevi,H. mani,H. pratensis,H. riparia,H. sturhaniandH. ustinovi, are morphologically closely related and represent theH. avenaespecies complex, and the other two,H. hordecalisandH. latipons, are morphologically more distinct from this complex. In this study we provide comprehensive phylogenetic analyses of several hundredCOIand ITS rRNA gene sequences from theAvenaegroup using Bayesian inference, maximum likelihood and statistical parsimony. Some 220COIand 11 ITS rRNA new gene sequences from 147 nematode populations collected in 26 countries were obtained in this study. Our study showed that theCOIgene is a powerful DNA barcoding marker for identification of populations and species from theAvenaegroup. A putatively new cyst nematode species related toH. latiponswas revealed from the analysis ofCOIand ITS rRNA gene datasets.COIgene sequences allow distinguishingH. arenaria,H. australisandH. sturhanifrom each other and other species. Problems of species delimiting of these species are discussed. The results of the analysis showed thatCOIhaplotypes corresponded to certain pathotypes of the cereal cyst nematodes. It is recommended that information onCOIhaplotypes of studied populations be included in research with these nematodes. Based on the results of phylogeographical analysis and age estimation of clades with a molecular clock approach, it was hypothesised that several species of theAvenaegroup primarily originated and diversified in the Irano-Anatolian hotspot during the Pleistocene and Holocene periods and then dispersed from this region across the world. Different geographic barriers, centres and times of origin might explain current known distribution patterns for species of theAvenaegroup. Possible pathways, including a long distance trans-Atlantic dispersal, and secondary centres of diversification are proposed and discussed.