| Odonia incana Rose, 1906 |
| Odonia viridiflora Rose, 1906 |
| Olivianae Krukoff & Barneby, 1974 |
| Olneya A. Gray, 1854 |
| Olneya tesota A. Gray, 1854 |
| Ononis L., 1753 |
| Ononis crotalarioides M.E. Jones, 1929 |
| Orbexilum Raf., 1832 |
| Orbexilum chiapasanum B.L. Turner, 2007 |
| Orbexilum melanocarpum (Benth. ex Hemsl.) Rydb., 1919 |
| Orbexilum oliganthum (Brandegee) B.L. Turner, 2007 |
| Ormosia Jack., 1811 |
| Ormosia apulensis Cortés, 1919 |
| Ormosia carinata N. Zamora, 2006 |
| Ormosia chlorocalyx Ducke, 1944 |
| Ormosia isthmensis Standl., 1937 |
| Ormosia macrocalyx Ducke, 1922 |
| Ormosia macrophylla Benth., 1837 |
| Ormosia mexicana Standl., 1922 |
| Ormosia oaxacana Rudd, 1981 |