[Wikipedia] Taxonomy: Many of what are known as varieties of Astragalus lentiginosus were originally described as individual species. Botanist Marcus E. Jones was the first to recognize the similarities among these taxa and arranged them as varieties of one species. Per Axel Rydberg employed a very different species concept stating that he did not believe in infrataxa. This resulted in his raising Jones's varieties to species in the genera Cystium and Tium. A notable novelty of Rydberg's treatment is the concept of sections which have been maintained in the keys of subsequent treatments, even if this was not explicitly stated. Subsequent treatments include Barneby, Isely, and Welsh. Each of these treatments are slightly different, containing between 36 and 42 taxa. Recent molecular work seems to suggest a genetic component to the varieties. (link added by Mary Ann Machi)