| Carex steyermarkii Standl., 1947 |
| Carex straminea Willd. ex Schkuhr, 1801 |
| Carex straminea var. australis L.H. Bailey, 1889 |
| Carex subfusca W. Boott, 1880 |
| Carex subulata J.F. Gmel., 1791 |
| Carex tehuacana Reznicek & S. González, 2021 |
| Carex tenejapensis Reznicek & S. González, 1999 |
| Carex tetrastachya Scheele, 1849 |
| Carex thurberi Dewey, 1859 |
| Carex tolucensis (F.J. Herm.) Reznicek, 1993 |
| Carex townsendii Mack., 1931 |
| Carex transmexicana Lois, Jim. Mejías, Acedo, S. González & Reznicek, 2025 |
| Carex tribuloides Wahlenb., 1803 |
| Carex tribuloides var. sangamonensis Clokey, 1919 |
| Carex triquetra Boott, 1846 |
| Carex tuberculata Liebm., 1850 |
| Carex tuberculata var. ehrenbergiana (Boeckeler) Kük., 1909 |
| Carex tuberculata var. tuberculata Liebm., 1850 |
| Carex tunimanensis Standl. & Steyerm., 1953 |
| Carex turbinata Liebm., 1850 |