| 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 subcordata (Benth. ex Oerst.) 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 |
| Ageratina tetragona (Schrad.) R.M. King & H. Rob., 1970 |
| Ageratina textitlana B.L. Turner, 2008 |
| Ageratina thomasii R.M. King & H. Rob., 1990 |
| Ageratina thyrsiflora (Greene) R.M. King & H. Rob., 1970 |
| Ageratina tomentella (Schrad.) R.M. King & H. Rob., 1970 |
| Ageratina trapezoides (Kunth) R.M. King & H. Rob., 1972 |
| Ageratina triangulata (DC.) B.L. Turner, 1987 |