The excel document “SeedplantSimulationData.xls” contains the supplemental data for the manuscript “Assessing Systematic Error in the Inference of Seed Plant Phylogeny” by J. G. Burleigh and S. Mathews. It has the full results of the parametric bootstrap analyses. The first page in the excel document gives the full results for the parametric bootstrap of the single locus data sets when the simulated data sets were analyzed using maximum parsimony (MP). Each locus was analyzed using all sites, just the RC23 sites, and just the RC4 sites. The tables are set up just like Table 1 in the manuscript. Five seed plant hypotheses were examined: GP = gnepine; GF = gnetifer; AN = anthophyte; GS = Gnetales sister to seed plants; GSG = Gnetales sister to gymnosperms. The columns with the seed plant hypotheses listed on top represent the seed plant hypothesis that was simulated; the rows represent the percentage of times each seed plant hypothesis was recovered from the simulated data sets. The row “other” represents the percentage of times a topology that is not consistent with any of the five listed seed plant hypotheses was recovered. . “BS” is the nonparametric bootstrap score obtained from the empirical data set. The bootstrap and adjusted bootstrap values from these analyses are listed in table 2a. The second page in the excel document gives the full results for the parametric bootstrap of the single locus data sets when the simulated data sets were analyzed using maximum likelihood (ML). Each locus was analyzed using all sites, just the RC23 sites, and just the RC4 sites. Again, the tables are set up just like Table 1 in the manuscript. Five seed plant hypotheses were examined: GP = gnepine; GF = gnetifer; AN = anthophyte; GS = Gnetales sister to seed plants; GSG = Gnetales sister to gymnosperms. The columns with the seed plant hypotheses listed on top represent the seed plant hypothesis that was simulated; the rows represent the percentage of times each seed plant hypothesis was recovered from the simulated data sets. The row “other” represents the percentage of times a topology that is not consistent with any of the five listed seed plant hypotheses was recovered. . “BS” is the nonparametric bootstrap score obtained from the empirical data set. The bootstrap and adjusted bootstrap values from these analyses are listed in table 2b. The third page lists the results for the parametric bootstrap of the 12-locus data sets. All the data from this page is found in Table 3 of the manuscript.