| Astragalus radicans var. harshbergeri (Rydb.) Barneby, 1964 |
| Astragalus radicans var. radicans Hornem., 1815 |
| Astragalus regiomontanus Barneby, 1964 |
| Astragalus reptans Willd., 1809 |
| Astragalus rosei M.E. Jones, 1923 |
| Astragalus rupertii Villarreal & M.A. Carranza, 1994 |
| Astragalus rusbyi Greene, 1884 |
| Astragalus rusbyi var. longissimus M.E. Jones, 1895 |
| Astragalus sabulonum A. Gray, 1878 |
| Astragalus sagitticarpus A.E. Estrada, Villarreal & Encina, 2020 |
| Astragalus saltonis M.E. Jones, 1923 |
| Astragalus sanctorum Barneby, 1976 |
| Astragalus sanguineus Rydb., 1929 |
| Astragalus scalaris S. Watson, 1888 |
| Astragalus scalaris var. quercetinus M.E. Jones, 1923 |
| Astragalus schaffneri M.E. Jones, 1923 |
| Astragalus scutaneus Barneby, 1956 |
| Astragalus seatonii M.E. Jones, 1895 |
| Astragalus seatonii var. crucis M.E. Jones, 1923 |
| Astragalus selenaeus Greene, 1895 |