Outcrossing rates and seed set were estimated at both the population and individual plant scale within four populations of Xanthorrhoea johnsonii. Sites differed with respect to habitat disturbance (time since ?re), plant density, mean plant height, and mean in?orescence length. Allozyme data from progeny arrays of 24 seeds per plant from ten plants at each site were used to determine maternal outcrossing rates, which were found to be consistently high at all sites (> 90%). Small but signi?cant levels of inbreeding were recorded at three of the four sites. There was close agreement between tm and ts measures, which indicated that most inbreeding was a result of within plant sel?ng rather than biparental inbreeding. Outcrossing rates were estimated within top, middle, and bottom thirds of spikes on six plants at a ?fth site. Signi?cant differences from complete outcrossing were recorded in the middle and/or bottom sections of three plants. Total seed set per plant and seed set per ?ower varied signi?cantly among the four sites. Xanthorrhoea johnsonii appears to be able to maintain relatively high outcrossing rates under different ecological conditions, although levels of both seed set per plant and seed set per ?ower are much more variable. 頲013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 335-345. ADDITIONAL KEYWORDS: ?owering density - fragmented populations - long-lived perennial - mating systems - plant age - seed set.