In a common-garden experiment, Polygonum cespitosum plants (N=660) from native- and introduced-range populations were grown under uniform, favorable conditions in a glasshouse and their traits compared. Introduced-range populations were sampled from the eastern USA (N=17), and native-range populations were sampled from a climate-matched region in northern Japan (N=18). Parental growing conditions were standardized prior to the experiment.

To characterize P. cespitosum's climatic distribution, principal component analyses of temperature- and precipitation-related variables were conducted using bioclimatic data extracted (from WorldClim) for species occurrence data.