Two new vagrant species of the genus Phytoptus Dujardin (Eriophyoidea, Phytoptidae, Phytoptinae) from Serbia are described: Phytoptus argenteus n. sp. from Potentilla argentea and P. serbicus n. sp. from Potentilla tommasiniana. Remarks on morphology of Phytoptus alchemillae Jočić et al. 2011 collected from Alchemilla plicata in Serbia and supplementary description of infrequently encountered species Phytoptus potentillae Chen et al. 2005 from Potentilla bifurca (Poaceae) based on mummies recovered from dry plant material from southern Russia are given. Sequences of mtCOI barcode region (658 bp) of three Phytoptus species (P. alchemillae, P. argenteus n. sp., and P. serbicus n. sp.) are provided. A brief comparison of pairwise genetic distances between congeneric eriophyoid mites across taxa of Eriophyoidea (including genus Phytoptus) indicates that COI sequences of congeneric eriophyoid mites do not precisely reflect phylogenetic relations of their hosts. This fact may be explained by (a) different rate of the COI evolution in different mite clades associated with phylogenetically related and unrelated hosts or by (b) similar timing of the associations between mites and plants (while having the same rate of COI evolution).