Common milkweed (Asclepias syriaca), the host plant of the Monarch butterfly, occurs across a wide geographic range in eastern North America.  Restoration efforts to support the declining Monarch populations involve planting milkweed to provide host plants for the caterpillars.  Informed choices of plant materials for restoration efforts require an understanding of the patterns and degree of divergence for traits that may be locally adapted.  The microsatellite study is part of a larger project testing for local adaption that is composed of two parts, 1) three large replicated common gardens in Minnesota, Ohio, and Virginia with seeds collected from throughout the native range that will provide data on growth, phenology and defenses that will be used to test hypotheses of local adaptation for biotic and abiotic factors over three seasons of growth, and 2) microsatellite analysis of the same populations grown in the common gardens to estimate the patterns of genetic structure and differentiation based on neutral markers. DNA was extracted from 260 greenhouse grown plants representing 30 populations including those grown in the three common gardens. Twelve microsatellite markers were used to estimate genetic variability and population structure.  Initial analysis using AMOVA indicates that 8% of variation is between populations, 26% among individuals, and 66% within individuals.  STRUCTURE and PCA analyses have not revealed significant structuring among the populations, and our results parallel a recent study using SNPs from genotype by sequencing that concluded that common milkweed populations across its native range are roughly panmictic (J.F Boyle et al., 2023, BioRvix preprint).  The common garden study is entering the third year of growth, and the results will be compared with microsatellites as neutral markers in Fst vs. Qst types of analyses to test hypotheses about local adaptation.