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In reward—producing animal—pollinated plants, small populations are likely to be less attractive to pollinators than large populations. The likelihood of pollinator limitation of seed production should therefore increase with decreasing population size. I documented the number of flowering plants and plant fecundity in 18 populations of the self—incompatible, tristylous herb Lythrum salicaria within an archipelago in northern Sweden in two consecutive years. To test the hypothesis that a positive correlation between population size and seed set is due to a higher degree of pollinator limitation in small than in large populations, I performed supplemental hand—pollinations in eight (1993) and 13 (1994) of the study populations. To test the hypothesis that common mating types are more likely than rare types to experience inadequate pollination, I compared the natural level of seed production and the effect of supplemental …