Allozyme markers were used to estimate mating system parameters in nine fragmented populations of the grassland daisy Rutidosis leptorrhynchoides that differed in size and spatial isolation. Multilocus estimates of outcrossing rate did not differ significantly among populations, all indicating a high level of outcrossing (tm=0·84–1·0). Small populations showed greater divergence than large populations between the allele frequencies in the population and those in the pollen pool, indicating paternal bottlenecks. Isolated populations of fewer than 200 individuals also exhibited higher correlations of outcrossed paternity (rp) than larger populations, indicating the production of more full-sibs within families. The combination of paternal bottlenecks and correlated paternity increases the genetic identity of progeny across families and predisposes populations to biparental inbreeding in subsequent generations. As over half the remaining populations of R. leptorrhynchoides contain fewer than 200 plants, such second-order inbreeding may threaten the viability of the species if it is associated with significant inbreeding depression.