| Ocellochloa stolonifera (Poir.) Zuloaga & Morrone, 2009 |
| Ochlopoa (Asch. & Graebn.) H. Scholz, 2003 |
| Ochlopoa annua (L.) H. Scholz, 2003 |
| Oedipachne Link, 1827 |
| Oedipachne punctata (L.) Link, 1827 |
| Oligosanthia Hitchc. & Chase, 1910 |
| Olmeca Soderstr., 1982 |
| Olmeca clarkiae (Davidse & R.W. Pohl) Ruiz-Sanchez, Sosa & Mejía-Saulés, 2011 |
| Olmeca fulgor (Soderstr.) Ruiz-Sanchez, Sosa & Mejía-Saulés, 2011 |
| Olmeca recta Soderstr., 1982 |
| Olmeca reflexa Soderstr., 1982 |
| Olmeca zapotecorum Ruiz-Sanchez, Sosa & Mejía-Saulés, 2011 |
| Olyra L., 1759 |
| Olyra arundinaceae Kunth, 1815 |
| Olyra axillaris Lam., 1797 |
| Olyra brasiliensis Desv., 1831 |
| Olyra brevifolia Schumach., 1827 |
| Olyra concinna Hook. f., 1896 |
| Olyra corcovadensis Wawra, 1866 |
| Olyra cordifolia Kunth, 1815 |