Centaurea solstitialis, yellow starthistle, is native to the Northern middle latitudes from the Mediterranean through Central Asia. The first herbarium specimens documented for the United States were collected in the late 1800's in the San Francisco Bay area. Because of the wide spread of the species into range and conservation lands in the Western United States, it is a good candidate for biocontrol. The project aims to improve the likelihood of finding appropriate biocontrol agents by estimating the origins of the United States populations, as well as determining if gene pools among the United States populations have mixed since their introductions. Sequence tagged microsatellite (STMS) markers were developed for Centaurea solstitialis as one tool in addressing these questions. Over seventy-five STMS primer pairs were screened for similarity in allele frequency and occurrence among Eurasian and United States populations.