| Oenothera suffulta (Engelm. ex A. Gray) W.L. Wagner & Hoch, 2007 |
| Oenothera suffulta subsp. nealleyi (J.M. Coult.) W.L. Wagner & Hoch, 2007 |
| Oenothera suffulta subsp. suffulta (Engelm. ex A. Gray) W.L. Wagner & Hoch, 2007 |
| Oenothera tamrae W. Dietr. & W.L. Wagner, 1987 |
| Oenothera tetraptera Cav., 1796 |
| Oenothera texensis P.H. Raven & D.R. Parn., 1970 |
| Oenothera thalassaphila Brandegee, 1922 |
| Oenothera toumeyi (Small) Tidestr., 1935 |
| Oenothera triloba Nutt., 1821 |
| Oenothera tubicula A. Gray, 1852 |
| Oenothera tubicula subsp. strigulosa (Towner) W.L. Wagner & Hoch, 2007 |
| Oenothera tubifera Ser., 1828 |
| Oenothera virgata Ruiz & Pav., 1802 |
| Oenothera wigginsii W.E. Klein, 1962 |
| Oenothera xenogaura W.L. Wagner & Hoch, 2007 |
| Oligospermum (Micheli) H. Hara, 1953 |
| Onagra Mill., 1754 |
| Onagraceae Juss., 1789 |
| Onagreae Dumort., 1827 |
| Onagroideae Eaton, 1836 |