| Ageratina resinifera H. Rob., 2001 |
| Ageratina rhodopoda (B.L. Rob.) R.M. King & H. Rob., 1970 |
| Ageratina rhomboidea (Kunth) R.M. King & H. Rob., 1970 |
| Ageratina riparia (Regel) R.M. King & H. Rob., 1970 |
| Ageratina riskindii B.L. Turner, 1987 |
| Ageratina rivalis (Greenm.) R.M. King & H. Rob., 1970 |
| Ageratina robinsoniana (Greene) B.L. Turner, 1987 |
| Ageratina rollinsii B.L. Turner, 1983 |
| Ageratina rothrockii (A. Gray) R.M. King & H. Rob., 1970 |
| Ageratina rubricaulis (Kunth) R.M. King & H. Rob., 1970 |
| Ageratina rufa (Greene) R.M. King & H. Rob., 1970 |
| Ageratina rupicola (B.L. Rob. & Greenm.) R.M. King & H. Rob., 1970 |
| Ageratina salicifolia R.M. King & H. Rob., 1978 |
| Ageratina saltillensis (B.L. Rob.) R.M. King & H. Rob., 1970 |
| Ageratina sandersii B.L. Turner, 1987 |
| Ageratina saxorum (Standl. & Steyerm.) R.M. King & H. Rob., 1991 |
| Ageratina schaffneri (Sch. Bip. ex B.L. Rob.) R.M. King & H. Rob., 1970 |
| Ageratina scorodonioides (A. Gray) R.M. King & H. Rob., 1970 |
| Ageratina seleri B.L. Turner, 1987 |
| Ageratina serboana B.L. Turner, 2007 |