Clonal individuals from 16 hemp dogbane populations with phenotypic variation were analyzed using isozyme and randomly amplified polymorphic DNA (RAPD) analysis. Plants originated from populations in Michigan and Illinois. Three known Apocynum species, spreading dogbane, hemp dogbane, and prairie dogbane, were evaluated. Genetic distance among populations was more pronounced with isozyme analysis compared to RAPD analysis. The combined isozyme and RAPD analysis data separated spreading dogbane from all other plants analyzed. Genetic variation was present among the 16 hemp dogbane populations, but was less than expected based on the phenotypic variation present among the collections. The short genetic distance between the 16 hemp dogbane collections and the three Apocynum species suggests that variation among populations of hemp dogbane may be from outcrossing with other closely related Apocynum species. Isozyme and RAPD analyses were also conducted on plants from two populations in Michigan to determine the level of genetic variation among plants within the same population. Genetic analysis revealed that one population was entirely clonal, while the other population was a mixture of clonal and segregating plants.