This ReadMe file describes “Amaranthus_Screening_Data.csv” and “Amaranthus_Seed_Production_and_Phenotype.csv”. Both files are comma-separated spreadsheets. The data were completely collected by Todd Gaines. Missing or non-collected data in both files are represented with a ‘.’ “Amaranthus_Screening_Data.csv” Column Headings: Plant: Species, refers to detailed accession information in Supplementary Table 1 Year: Year of field experiment, or GH for greenhouse Lab ID: individual plant ID number, corresponds to Amaranthus Seed Production and Phenotype.csv Distance (m) from pollen source #: the distance in meters that the individual plant was from the glyphosate-resistant A. palmeri pollen source seeds per gram: measured on harvested seed samples Run: indicates experimental run 1 or 2 g planted: grams of seed planted in each replication Replication: 5 replications per experimental run per individual plant Estimated # Emerged: number of emerged seedlings in each replication % Emerged: based on emerged number of seedlings and estimated number of seed planted # Hybrids: number of individual confirmed hybrid plants, confirmation made using EPSPS copy number and species-diagnostic molecular markers, as indicated in Table 3 in the publication % Hybrids (of Emerged): the percentage of emerged seedlings confirmed as hybrids “Amaranthus_Seed_Production_and_Phenotype.csv” Column Headings: Year: Year field experiment conducted Lab ID: Individual plant number, corresponds to Lab ID in Amaranthus Screening Data.csv Distance (m) from pollen source : the distance in meters that the individual plant was from the glyphosate-resistant A. palmeri pollen source Plant: Species, corresponds to detailed accession information in Supplementary Table 1 # seeds per gram: Used to calculate total number of seeds Height (cm): measured at harvest Stem circumference (cm): measured at harvest Seed weight (g): total weight of seeds from plant Seeds per Sample: total calculated number of seeds from each plant Total Plant Weight (g): measured at harvest