| Cinnagrostis Griseb., 1874 |
| Cinnastrum (E. Fourn.) Pilg., 1956 |
| Claudia Opiz, 1853 |
| Cleachne Roland ex Rottb., 1778 |
| Clinelymus (Griseb.) Nevski, 1931 |
| Clinelymus canadensis (L.) Nevski, 1932 |
| Clinelymus glaucus (Buckley) Nevski, 1932 |
| Clinelymus glaucus subsp. californicus Nevski, 1932 |
| Clinelymus glaucus subsp. coloratus Nevski, 1932 |
| Clomena P. Beauv., 1812 |
| Clomena (P. Beauv.) Pilg., 1956 |
| Clomena peruviana P. Beauv., 1812 |
| Clomena peruviana var. pulvinata Nees, 1841 |
| Coelorachis Brongn., 1829 |
| Coelorachis aurita (Steud.) A. Camus, 1921 |
| Coelorachis ramosa (E. Fourn.) Nash, 1909 |
| Coelorachis rugosa (Nutt.) Nash, 1909 |
| Coicinae Clayton & Renvoize, 1986 |
| Coix L., 1753 |
| Coix agrestis Lour., 1790 |