Phylogenetic relationships in the genus Festuca, as expressed in recent classification systems, were tested using chloroplast DNA restriction endonuclease site variation data. Species native or introduced to North America were used as exemplars for taxa related to Festuca that have been recognized variously as genera, subgenera, and (or) sections. Cladistic analysis of 67 shared chloroplast DNA restriction site mutations indicated that Festuca and some related taxa, as circumscribed in morphologically based classifications, appear to be non-monophyletic. Cluster analysis of 108 polymorphic sites was largely congruent with the results of the cladistic analysis. Two main evolutionary lines were indicated. One contained the majority of the genus Festuca exemplars, including the subgenera Drymanthele, Subulatae, Subuliflorae, Obtusae, and Festuca, as well as Vulpia, Argillochloa, and subg. Leucopoa sect. Breviaristatae. The other lineage included subgenus Schedonorus, subg. Leucopoa sect. Leucopoa, and the genus Lolium. Analyses supported the recognition of two genera in each lineage: Vulpia and Festuca in one, and Leucopoa sensu stricto (including only sect. Leucopoa) and Lolium (including Festuca subg. Schedonorus) in the other. The recognition of the monotypic generic segregate Argillochloa (= F. dasyclada) was not supported by the analyses. Key words: Festuca, Leucopoa, Lolium, Vulpia, phylogeny, chloroplast DNA.