| 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 |
| Ageratina sinaloensis R.M. King & H. Rob., 1978 |
| Ageratina skutchii (B.L. Rob.) R.M. King & H. Rob., 1970 |
| Ageratina soejimana B.L. Turner, 2008 |
| Ageratina solana B.L. Turner, 2008 |
| Ageratina sousae B.L. Turner, 1987 |
| Ageratina spooneri B.L. Turner, 2008 |
| Ageratina stricta (A. Gray) R.M. King & H. Rob., 1970 |
| Ageratina subcoriacea R.M. King & H. Rob., 1990 |
| Ageratina subinclusa (Klatt) R.M. King & H. Rob., 1978 |
| Ageratina subpenninervia (Sch. Bip. ex Klatt) R.M. King & H. Rob., 1977 |
| Ageratina sundbergii B.L. Turner, 1986 |
| Ageratina tejalapana B.L. Turner, 2013 |