| 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 |
| Carex tuxtleca Lois, Jim. Mejías, Acedo, S. González & Reznicek, 2025 |
| Carex ultra L.H. Bailey, 1886 |
| Carex underwoodii Britton, 1905 |
| Carex utriculata Boott, 1839 |
| Carex vallicola Dewey, 1861 |
| Carex vallicola var. hidalgensis F.J. Herm., 1960 |
| Carex venosivaginata Standl. & Steyerm., 1953 |