A polyphasic taxonomic study was performed to compare 26 novel bacterial isolates obtained from (semi-)natural grassland soils and a heathland soil in the Netherlands with 16 strains that had previously been assigned to the genus Collimonas. Genomic fingerprinting (BOX-PCR), whole-cell protein electrophoresis, matrix-assisted laser desorption ionization time-of-flight mass spectrometry of intact cells and physiological characterization (Biolog) of the isolates confirmed the existence of different strain clusters (A-D) within the genus Collimonas. Until now, only cluster C strains have been formally classified, as Collimonas fungivorans. In this study, DNA-DNA hybridizations were performed with a selection of strains representing the four clusters. The results showed that cluster B strains also belong to C. fungivorans and that strains of clusters A and D represent two novel species within the genus Collimonas. The latter novel species could be differentiated by means of phenotypic and genotypic characteristics and are classified as Collimonas arenae sp. nov. (cluster A; type strain Ter10(T) =LMG 23964(T) =CCUG 54727(T)) and Collimonas pratensis sp. nov. (cluster D; type strain Ter91(T) =LMG 23965(T) =CCUG 54728(T)).