Separate introductions or post-introduction evolutionary processes in invasive species may generate multiple genotypes or varying ploidies that differ in their response (phenotype) to a range of environments. Increased ploidy is predicted to be positively correlated with phenotypic plasticity, but support for this relationship is mixed. Positive response to sediment N or P enrichment varies between species but may contribute to invasiveness if a species (or genotype) has greater plasticity to increased resource availability. The way in which genetic variation and associated phenotypic plasticity between introduced plant populations determines response to N or P is unknown for most invaders but could be important in explaining variability in the spread and subsequent impacts by invaders with multiple introduced lineages. We conducted a common garden experiment, in which ten populations (diploid and triploid cytotypes) of the Eurasian invasive plant, Butomus umbellatus were grown under varying N-P nutrient levels (4, 40, 200, 400 mg/L N; 0.4, 4, 40 mg/L P). We measured reaction norms for biomass accumulation, vegetative reproduction, nutrient allocation. Diploid populations produced, on average, 300% more aboveground biomass and 250% more reproductive biomass at high [N] and 200% more aboveground biomass and 250% more reproductive biomass across [P]. In contrast, triploid plants produced 30% and 150% more underground biomass than diploid plants, in response to N and P, respectively. Tissue chemistry in response to N or P was similar between cytotypes for C, N, P C:N was consistently lower in triploid plants regardless of nutrient treatment. Diploid plants outperformed triploid plants at all [P] and all but the lowest [N] in biomass measures except underground biomass, a feature which may contribute to the successful invasion of the triploid cytotype in the US Pacific Northwest.