Separate introductions or post-introduction evolution may lead to multiple invader genotypes or cytotypes that differ in growth rates, biomass or chemical profile responses (phenotype) to a range of environments. If the invader has high trait plasticity to a range of resource levels, then sediment N or P enrichment may enhance invasiveness. However, the ways in which ploidy, plasticity, and available N or P interact is unknown for most species despite the potential to explain spread and impacts by invaders with multiple introduced lineages. We conducted a common garden experiment with four triploid and six diploid populations of Butomus umbellatus, collected from across its invasive range in the United States. Plants were grown under different N or P nutrient levels (4, 40, 200, 400 mg/L N; 0.4, 4, 40 mg/L P) and we measured reaction norms for biomass, clonal reproduction, and tissue chemistry. Contrary to our expectation, triploid B. umbellatus plants were less plastic to variation in N or P than diploid B. umbellatus in most measured traits. Diploid plants produced 172% more reproductive biomass and 57% more total biomass across levels of N, and 158% more reproductive biomass and 33% more total biomass across P than triploid plants. Triploid plants had lower shoot:root ratios and produced 30% and 150% more root biomass than diploid plants in response to increases in N and P, respectively. Tissue chemistry differed between cytotypes but plasticity was similar; N was 8% higher and C:N ratio was 30% lower in triploid than diploid plants across levels of N and plant parts, and N was 22% higher and C:N ratio 27% lower across levels of P and plant parts. Our results highlight differences in nutrient response between cytotypes of a widespread invader, and we call for additional field studies to better understand the interaction of nutrients and ploidy during invasion.