| Carex interior f. keweenawensis (F.J. Herm.) Fernald, 1942 |
| Carex interior var. keweenawensis F.J. Herm., 1941 |
| Carex interjecta Reznicek, 1993 |
| Carex involucrata Boeckeler, 1855 |
| Carex involucratella Mack., 1931 |
| Carex ixtapalucensis S. González ex Reznicek, 1986 |
| Carex jamesonii Boott, 1845 |
| Carex jamesonii var. chordalis (Liebm.) Kük., 1909 |
| Carex jamesonii var. gracilis L.H. Bailey, 1888 |
| Carex jamesonii var. melanosperma (Liebm.) Kük., 1909 |
| Carex jovis C.B. Clarke, 1908 |
| Carex kelloggii W. Boott, 1880 |
| Carex kelloggii var. kelloggii W. Boott, 1880 |
| Carex koyamae (Gómez-Laur.) J.R. Starr, 2015 |
| Carex laevivaginata (Kük.) Mack., 1913 |
| Carex lagunensis M.E. Jones, 1933 |
| Carex latebrosa Mack., 1907 |
| Carex lativena S.D. Jones & G.D. Jones, 1993 |
| Carex leporina L., 1753 |
| Carex leporina var. bracteata Liebm., 1850 |