Unisexual (all female) salamanders in the genus Ambystoma are animals of variable ploidy (2N-5N) that reproduce via a unique system of ‘leaky’ gynogenesis. As a result, these salamanders have a diverse array of nuclear genome combinations from up to five sexual species: the blue-spotted (A. laterale), Jefferson (A. jeffersonianum), smallmouth (A. texanum), tiger (A. tigrinum) and streamside (A. barbouri) salamanders. Identifying the genome complement, or biotype, is a critical first step in addressing a broad range of ecological and evolutionary questions about these salamanders. Previous work relied upon genome-related differences in allele size distributions for specific microsatellite loci, but overlap in these distributions among different genomes makes definitive identification and ploidy determination in unisexuals difficult or impossible. Here, we develop the first single nucleotide polymorphism assay for the identification of unisexual biotypes, based on species-specific nucleotide polymorphisms in noncoding DNA loci. Tests with simulated and natural unisexual DNA samples show that this method can accurately identify genome complement and estimate ploidy, making this a valuable tool for assessing the genome composition of unisexual samples.