| Astragalus sinaloae Barneby, 1964 |
| Astragalus sonorae A. Gray, 1853 |
| Astragalus spellenbergii A.E. Estrada, S. González & Villarreal, 2016 |
| Astragalus stenophyllus Torr. & A. Gray, 1838 |
| Astragalus stenophyllus var. filipes (Torr. & A. Gray) Tidestr., 1937 |
| Astragalus stenophyllus var. residuus (Jeps.) Barneby, 1950 |
| Astragalus stictocarpus (Rydb.) Tidestr., 1937 |
| Astragalus streptopus Greene, 1885 |
| Astragalus strigulosus Kunth, 1823 |
| Astragalus strigulosus var. brevidentatus Hemsl., 1879 |
| Astragalus strigulosus var. gracilis Hemsl., 1879 |
| Astragalus subuniflorus Greene, 1910 |
| Astragalus tephrodes A. Gray, 1853 |
| Astragalus tepicus E. Sheld., 1894 |
| Astragalus terlinguensis Cory, 1937 |
| Astragalus texanus E. Sheld., 1894 |
| Astragalus thurberi A. Gray, 1854 |
| Astragalus tijuanensis A.E. Estrada, Rebman, C. González & Villarreal, 2022 |
| Astragalus tioides (Rydb.) Barneby, 1964 |
| Astragalus tolucanus B.L. Rob. & Seaton, 1893 |