| Alvordia glomerata var. insularis A.M. Carter, 1964 |
| Amauria Benth., 1844 |
| Amauria brandegeeana (Rose) Rydb., 1914 |
| Amauria carterae A.M. Powell, 1972 |
| Amauria dissecta A. Gray, 1849 |
| Amauria rotundifolia Benth., 1844 |
| Amauriopsis Rydb., 1914 |
| Amauriopsis autumnalis (W.L. Ellison) B.L. Turner, 2010 |
| Amauriopsis dissecta (A. Gray) Rydb., 1914 |
| Amauriopsis glandulosa (Greenm.) B.L. Turner, 2010 |
| Amauriopsis janakosiana B.L. Turner, 2010 |
| Amauriopsis pedata (A. Gray) B.L. Turner, 2010 |
| Amblyolepis DC., 1836 |
| Amblyolepis setigera DC., 1836 |
| Amblyopappus Hook. & Arn., 1841 |
| Amblyopappus pusillus Hook. & Arn., 1841 |
| Ambrosia L., 1753 |
| Ambrosia acanthicarpa Hook., 1834 |
| Ambrosia acuminata (Brandegee) W.W. Payne, 1964 |
| Ambrosia ambrosioides (Cav.) W.W. Payne, 1964 |