| Neonelsonia ovata J.M. Coult. & Rose, 1895 |
| Niphogeton Schltdl., 1857 |
| Oenanthe L., 1753 |
| Oenanthe pringlei J.M. Coult. & Rose, 1895 |
| Oreomyrrhis Endl., 1839 |
| Oreomyrrhis orizabae I.M. Johnst., 1938 |
| Oreomyrrhis tolucana I.M. Johnst., 1938 |
| Osmorhiza Raf., 1819 |
| Osmorhiza bipatriata Constance & R.H. Shan, 1948 |
| Osmorhiza geohintonii B.L. Turner, 2011 |
| Osmorhiza mexicana Griseb., 1879 |
| Osmorhiza mexicana subsp. bipatriata (Constance & R.H. Shan) Lowry & A.G. Jones, 1985 |
| Osmorhiza mexicana subsp. mexicana Griseb., 1879 |
| Ottoa Kunth, 1821 |
| Ottoa oenanthoides Kunth, 1821 |
| Pastinaca L., 1753 |
| Pastinaca sativa L., 1753 |
| Pentacrypta Lehm., 1829 |
| Pentacrypta atropurpurea Lehm., 1828 |
| Perideridia Rchb., 1837 |