Twelve populations of Nacobbus aberrans, sensu lato, from Mexico, Bolivia, Peru, Ecuador and Argentina were subjected to molecular analysis of their genetic variability. RFLP banding patterns revealed three groups: i) Mexico, Ecuador and Argentina 1 populations; ii) Bolivia and Peru populations; iii) Argentina 2 population. These differences were confirmed by sequencing the ITS rDNA region. Depth of branching was strongly supportive of the presence of three separate species, thus supporting the hypothesis that N. aberrans s.l. is indeed a species complex. The populations from Mexico, Ecuador and Argentina 1 are attributed to N. aberrans s.s., although this requires confirmation by molecular characterisation of N. aberrans from the type locality in the USA; those from Bolivia and Peru are attributed to N. bolivianus Lordello, Zamith & Boock, 1961 with Argentina 2 regarded as representing another taxon. Nacobbus serendipiticus and N. batatiformis are removed from synonymy under N. aberrans s.l . and regarded as species inquirendae . Consistent minor banding patterns in the RFLP profiles may indicate that the genus reproduces predominantly by parthenogenesis.