| Panicum olyroides Kunth, 1816 |
| Panicum onslowense Ashe, 1900 |
| Panicum onurus Willd. ex Trin., 1834 |
| Panicum orangense Ashe, 1899 |
| Panicum oricola Hitchc. & Chase, 1906 |
| Panicum orientale (Rich.) Willd., 1809 |
| Panicum orinocense Willd. ex Spreng., 1825 |
| Panicum ornatum Desv. ex Ham., 1825 |
| Panicum orthophyllum Ashe, 1900 |
| Panicum oryzoides Sw., 1788 |
| Panicum ovale Elliott, 1816 |
| Panicum ovale var. addisoniii (Nash) C.F. Reed, 1989 |
| Panicum ovale var. pseudopubescens (Nash) Lelong, 1984 |
| Panicum ovale var. villosum (A. Gray) Lelong, 1984 |
| Panicum ovinum Scribn. & J.G. Sm., 1899 |
| Panicum owenae E.P. Bicknell, 1908 |
| Panicum pacificum Hitchc. & Chase, 1910 |
| Panicum pallens Sw., 1788 |
| Panicum pallens var. angustifolium Rupr., 1842 |
| Panicum pallens var. majus Nees, 1829 |