Previous studies have shown hybridization to occur between two Amaranthus species, Palmer amaranth and common waterhemp.  However, our preliminary observations have suggested that seeds obtained from controlled crosses between these two dioecious species may not always be hybrids. Thus, the objective of this study was to more rigorously evaluate putative hybrids between these two species. Sixty-nine progeny were evaluated from two Palmer amaranth females mated with common waterhemp. To determine if the progeny were hybrids, they were evaluated for the presence of a common waterhemp acetolactate synthase (ALS) allele and for nuclear DNA content. Palmer amaranth and common waterhemp have 2C DNA contents of 0.9 and 1.4 pg, respectively, and, therefore, nuclear DNA content analysis via flow cytometry is a robust means to distinguish among the parental species and their hybrids. General morphology and sex identity (male or female) were also scored for each progeny. Sixty of the 69 progeny did not have a common waterhemp ALS allele and had DNA contents similar to that of parental Palmer amaranth. Furthermore, these progeny were all females. Possibly these progeny were the result of agamospermy. Of the nine progeny that were heterozygous at the ALS locus - and thus obtained via hybridization - eight died before reaching reproductive growth or were sterile. Cytogenetic evaluation of the one hybrid that allowed for continued introgression indicated it was a triploid. Our results confirmed that hybrids between Palmer amaranth and common waterhemp can be obtained, but many progeny from controlled crosses between these two species do not allow for continued gene introgression.