| Oreocosmus galeottianus Naudin, 1850 |
| Oreocosmus monticola Naudin, 1850 |
| Osbeckia L., 1753 |
| Osbeckia pumila (Bonpl.) DC., 1828 |
| Ossaea DC., 1828 |
| Ossaea ciliata Cogn., 1891 |
| Ossaea disparilis Standl., 1933 |
| Ossaea micrantha (Sw.) Macfad. ex Cogn., 1891 |
| Ossaea trichocalyx Pittier, 1923 |
| Oxymeris DC., 1828 |
| Oxymeris cornoides Triana, 1871 |
| Oxymeris dichotoma (Pav. ex D. Don) Triana, 1872 |
| Oxymeris melanodesma (Naudin) Triana, 1871 |
| Oxymeris multiplinervis (Naudin) Triana, 1871 |
| Pleroma D. Don, 1823 |
| Pleroma galeottianum Triana, 1871 |
| Pleroma longifolium (Vahl) Triana, 1871 |
| Pleroma mexicanum DC., 1828 |
| Pleroma naudinianum Triana, 1871 |
| Pleroma rufipile Triana, 1871 |