There are three files containing genotype data from 12 microsatellite (SSR) loci for 412 individuals from 14 Lolium perenne ssp. multiflorum populations from California: LoliumSSRgenepop : genepop file format for easy conversion to other formats LoliumSSRstructure : formatted for analysis with STRUCTURE software. 1 column format, missing data is coded as -9 LoliumSSRgenalex : formatted for analysis with Genalex package in Excel software. 2 column format, missing data is coded as 0. The first tab “Lolium genotypes” contains genotype and population data. The second tab “Lolium population locations” contains latitude and longitude coordinates.