The 'Lactobacillus plantarum group' encompasses the taxa Lactobacillus plantarum subsp. plantarum, Lactobacillus plantarum subsp. argentoratensis, Lactobacillus paraplantarum, Lactobacillus pentosus and Lactobacillus arizonensis. In this study, the phylogenetic position of L. arizonensis was examined using 16S rRNA gene-specific methodologies (16S rRNA sequencing and ribotyping) and genomic DNA-based investigations [repetitive extragenic palindromic DNA (rep)-PCR and DNA-DNA hybridization]. Our results show that the L. arizonensis type strain could not be distinguished from the type strain of L. plantarum or from various L. plantarum reference strains. Therefore, it is proposed that the species L. arizonensis should be reclassified as a heterotypic synonym of L. plantarum.