| Eupatorium nubigenoides B.L. Rob., 1906 |
| Eupatorium nubigenum Benth., 1841 |
| Eupatorium nubivagum L.O. Williams, 1975 |
| Eupatorium nutans Kunth, 1818 |
| Eupatorium oaxacanum Klatt, 1882 |
| Eupatorium odoratum L., 1759 |
| Eupatorium oerstedianum Benth., 1853 |
| Eupatorium oliganthes Less., 1830 |
| Eupatorium oligocephalum DC., 1836 |
| Eupatorium omphaliifolium Kunth & C.D. Bouché, 1844 |
| Eupatorium opadoclinium (S.F. Blake) McVaugh, 1972 |
| Eupatorium oreithales Greenm., 1897 |
| Eupatorium oresbioides B.L. Rob., 1909 |
| Eupatorium oresbium B.L. Rob., 1900 |
| Eupatorium orizabae Sch. Bip. ex Hemsl., 1881 |
| Eupatorium ornatum (R.M. King & H. Rob.) B.L. Turner, 1997 |
| Eupatorium ortegae B.L. Rob., 1923 |
| Eupatorium ovaliflorum Hook. & Arn., 1838 |
| Eupatorium ovandense Grashoff & Beaman, 1969 |
| Eupatorium ovatifolium Hieron., 1908 |