| Adenothamnus validus (Brandegee) D.D. Keck, 1935 |
| Adopogon Neck. ex Kuntze, 1891 |
| Aganippea Moc. & Sessé ex DC., 1837 |
| Aganippea bellidiflora Moc. & Sessé ex DC., 1837 |
| Agassizia A. Gray & Engl., 1847 |
| Agassizia suavis A. Gray & Engl., 1847 |
| Ageratella A. Gray ex S. Watson, 1887 |
| Ageratella microphylla (Sch. Bip.) A. Gray ex S. Watson, 1887 |
| Ageratella microphylla var. microphylla (Sch. Bip.) A. Gray ex S. Watson, 1887 |
| Ageratella microphylla var. palmeri A. Gray, 1887 |
| Ageratella microphylla var. seemannii (Benth. & Hook. f.) A. Gray, 1887 |
| Ageratella microphylla var. sonorana B.L. Turner, 1995 |
| Ageratella palmeri (A. Gray) B.L. Rob., 1905 |
| Ageratina Spach, 1841 |
| Ageratina abronia (Klatt) R.M. King & H. Rob., 1972 |
| Ageratina acevedoana B.L. Turner, 1993 |
| Ageratina acutidentata (B.L. Rob.) R.M. King & H. Rob., 1970 |
| Ageratina adenachaenia (Sch. Bip. ex Klatt) R.M. King & H. Rob., 1970 |
| Ageratina adenophora (Spreng.) R.M. King & H. Rob., 1970 |
| Ageratina aegirophylla (B.L. Rob.) R.M. King & H. Rob., 1970 |