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Abstract The rapid pace of contemporary environmental change puts many species at risk, especially rare species constrained by limited capacity to adapt or migrate due to low genetic diversity and/or fitness. But the ability to acclimate can provide another way to persist through change. We compared the capacity of rareBoechera perstellata(Braun's rockcress) and widespreadB. laevigatato acclimate to change. We investigated the phenotypic plasticity of growth, biomass allocation, and leaf morphology of individuals ofB. perstellataandB. laevigatapropagated from seed collected from several populations throughout their ranges in a growth chamber experiment to assess their capacity to acclimate. Concurrently, we assessed the genetic diversity of sampled populations using 17 microsatellite loci to assess evolutionary potential. Plasticity was limited in both rareB. perstellataand widespreadB. laevigata, but differences in the plasticity of root traits between species suggest thatB. perstellatamay have less capacity to acclimate to change. In contrast to its widespread congener,B. perstellataexhibited no plasticity in response to temperature and weaker plastic responses to water availability. As expected,B. perstellataalso had lower levels of observed heterozygosity thanB. laevigataat the species level, but population‐level trends in diversity measures were inconsistent due to high heterogeneity amongB. laevigatapopulations. Overall, the ability of phenotypic plasticity to broadly explain the rarity ofB. perstellataversus commonness ofB. laevigatais limited. However, some contextual aspects of our plasticity findings compared with its relatively low genetic variability may shed light on the narrow range and habitat associations ofB. perstellataand suggest its vulnerability to climate warming due to acclimatory and evolutionary constraints.