Variation in patterns of mating within and among plant populations can be impacted by habitat disturbance and have significant implications for offspring fitness. An understanding of this variation will inform predictions of seed genetic quality, benefiting ecological restoration through better seed-sourcing guidelines. We assessed mating system variation in six populations of tuart (Eucalyptus gomphocephala DC.), an iconic tree of significance to ecological restoration in Western Australia. A mixed mating system was observed with predominant outcrossing (tm≤0.76±0.05) and low biparental inbreeding (tm-ts≤0.03±0.02). We detected some evidence of increased inbreeding in a naturally fragmented population (tm-ts≤0.10±0.04) and in a disturbed urban remnant (tm≤0.52±0.12), including a family with complete selfing. However, most variation in outcrossing rate occurred among individuals within populations (82%), rather than among populations (2.6%) or among groups of populations defined by fragmentation or disturbance (15.4%). Genetic diversity was not consistently lower in offspring from fragmented, smaller and/or disturbed populations. These data reinforce the importance of sourcing seeds from multiple trees for ecological restoration, and emphasise that tuart's mating system and the genetic diversity of offspring is robust to some habitat disturbance and/or fragmentation. © CSIRO 2013.