Patterns of clonal diversity in parthenogenetic species can be influenced by occasional sexual reproduction, selection due to environmental heterogeneity, and genetic drift. Here we investigate geographic patterns of clonal diversity in the obligate parthenogenetic earth mite species, Penthaleus major, in southeastern Australia. Spatial autocorrelation analysis indicated a relationship between geographic distance and clonal diversity at the sites. However, there was no evidence for an association between distance and clonal composition or the frequency of the two most common clones. Regression analyses indicated that clonal diversity and the frequency of one of the common clonal groups were associated with latitude and/or climatic variables, whereas the other common group was not associated with any of those variables. In four transects (each 250–400 km in length) extending from the center of the distribution of P. major to its margins, there was a consistent and continuous decline in clonal diversity as the margin was approached but no evidence that one clonal group predominated at the margin. This argues against the importance of a general-purpose genotype being favored at margins and suggests that either selection acts to decrease local diversity at sites near the margin or that diversity declines due to drift at these sites.