| Aristida purpurea var. wrightii (Nash) Allred, 1984 |
| Aristida purpusiana Hitchc., 1913 |
| Aristida racemosa Muhl., 1817 |
| Aristida rariflora (Hitchc.) Henrard, 1927 |
| Aristida recurvata Kunth, 1816 |
| Aristida reverchonii Vasey, 1886 |
| Aristida reverchonii var. angusta Vasey, 1892 |
| Aristida roemeriana Scheele, 1849 |
| Aristida sanctae-luciae Trin., 1826 |
| Aristida scabra (Kunth) Kunth, 1829 |
| Aristida schaffneri E. Fourn., 1885 |
| Aristida schiedeana Trin. & Rupr., 1842 |
| Aristida schiedeana var. minor Vasey, 1886 |
| Aristida schiedeana var. orcuttiana (Vasey) Allred & Valdés-Reyna, 1995 |
| Aristida schiedeana var. schiedeana Trin. & Rupr., 1842 |
| Aristida scribneriana Hitchc., 1924 |
| Aristida secunda Rud. ex Roem. & Schult., 1817 |
| Aristida simpliciflora Chapm., 1878 |
| Aristida simpliciflora var. texana Vasey, 1892 |
| Aristida sorzogonensis J. Presl, 1830 |