| Oldenlandia microtheca (Schltdl. & Cham.) DC., 1830 |
| Oldenlandia ovata S. Watson, 1883 |
| Oldenlandia pringlei B.L. Rob., 1892 |
| Oldenlandia repens L., 1767 |
| Oldenlandia rubra (Cav.) A. Gray, 1853 |
| Oldenlandia xestosperma B.L. Rob. & Greenm., 1896 |
| Oldenlandiopsis Terrell & W.H. Lewis, 1990 |
| Oldenlandiopsis callitrichoides (Griseb.) Terrell & W.H. Lewis, 1990 |
| Omiltemia Standl., 1918 |
| Omiltemia filisepala (Standl.) C.V. Morton, 1968 |
| Omiltemia guerrerensis Lozada-Pérez & J. Rojas, 2016 |
| Omiltemia longipes Standl., 1918 |
| Omiltemia parvifolia Borhidi & K. Velasco, 2010 |
| Omiltemia scoti J.H. Kirkbr., 1984 |
| Ophiorrhiza L., 1753 |
| Ophiorrhiza mitreola L., 1753 |
| Ophiorrhizeae Bremek. ex Verdc., 1958 |
| Ophryococcus Oerst., 1852 |
| Paederia L., 1767 |
| Paederia ciliata (Bartl. ex DC.) Standl., 1940 |