Michaux's sumac (Rhus michauxii) is a federally endangered rhizomatous shrub endemic to the southeastern United States, with two of the largest populations located at Maneuver Training Center--Fort Pickett, VA (Fort Pickett), and a nearby property, Deepwater. Michaux's sumac requires soil disturbance and fire to maintain healthy populations. Before being added to the endangered species list, 47% of populations were extirpated due to habitat loss, fire suppression, and hybridization with smooth sumac (Rhus glabra). Concerns with hybridization include hybrid swamping if hybrids are fertile, or outbreeding depression if hybrids display reduced fitness. I used genotyping-by-sequencing to estimate the extent of hybridization at Fort Pickett and Deepwater, and to assess how such hybridization may impact survival of Michaux's sumac as a distinct species at each of these locations. Additionally, population structure was examined using DAPC (discriminant analysis of principal components) and Admixture analyses to determine whether the colonies at Fort Pickett and Deepwater make up separate populations, meta-populations, or one large population. Analysis of 107,344 SNPs (single nucleotide polymorphisms) using Introgress and Admixture software suggested widespread hybridization at both Fort Pickett and Deepwater, with hybrids present in most of the sampled colonies. Population structure analyses revealed differentiation between the Fort Pickett and Deepwater populations, but little evidence of separate populations among the colonies sampled at Fort Pickett. These results are important for conservation planning to ensure the long-term survival of Michaux's sumac at Fort Pickett and Deepwater and can be used to help inform future management decisions. / Master of Science / Michaux's sumac (Rhus michauxii) is a small, federally endangered shrub endemic to the southeastern United States, with populations remaining in North Carolina, Virginia, and Georgia. To date, the largest known colonies of Michaux's sumac are in Virginia at Maneuver Training Center--Fort Pickett, VA (Fort Pickett), and at a nearby privately owned property called Deepwater. Michaux's sumac requires soil disturbance and fire to reduce competition and maintain healthy populations. It currently faces threats from habitat loss due to agricultural land use and fire suppression, and hybridization with a closely related species, smooth sumac (Rhus glabra). Hybridization is a threat to Michaux's sumac at Fort Pickett and Deepwater because it co-occurs with smooth sumac throughout the area. This study determined how much smooth sumac and Michaux's sumac are hybridizing in these locations and assessed whether hybridization is a threat to the long-term survival of the populations at each site. A secondary goal of the study was to gain a better understanding of how genetically similar the colonies within and between locations are to one another. Understanding the level of hybridization and the population structure of Michaux's sumac is important for making management decisions to protect the species. I found widespread hybridization between Michaux's and smooth sumac, with hybrid individuals at nearly all the colonies sampled. Additionally, there is evidence that Fort Pickett and Deepwater comprise two distinct populations, but the colonies inside each area are likely not separate populations. These results will inform future conservation management decisions for the species.