A 1977 Masters research project done by a Texas resident, John Williams, titled "Biosystematic Study of a Desmodium Complex," aimed to sort out the interrelationships between the three species that have been commonly confused in the past -- D. canescens, D. tweedyi, and D illinoense. Using morphological evidence, reproductive biology, cytological evidence (chromosome counts), and palynological evidence (pollen size and shape), this researcher concluded that the two species that really are close are the former two, with D. illinoense the outlier; in fact, based on cross-breeding of the former two, he offered a new scientific name: Desmodium canescens var. tweedyi (Britt.) Williams. This researcher concluded the following: "The data suggest that D. tweedyi is not a distinct species but rather that it is more likely a geographical variant (the southwestern extreme) of D. canescens." That assessment has not become definitive, but this illustrates the challenges a plant collector faces with a genus with very similar species.
