| Abasoloa La Llave, 1824 |
| Acanthambrosia Rydb., 1922 |
| Acanthambrosia bryantii (Curran) Rydb., 1922 |
| Acanthospermum Schrank, 1819 |
| Acanthospermum australe (Loefl.) Kuntze, 1891 |
| Acanthospermum hispidum DC., 1836 |
| Acanthospermum humile (Sw.) DC., 1836 |
| Acarphaea Harv. & A. Gray ex A. Gray, 1849 |
| Acarphaea artemisiifolia Harv. & A. Gray, 1849 |
| Achaenipodium Brandegee, 1906 |
| Achaenipodium discoideum Brandegee, 1906 |
| Achaetogeron A. Gray, 1849 |
| Achaetogeron affinis A. Gray, 1886 |
| Achaetogeron ascendens Greenm., 1905 |
| Achaetogeron corymbosus Larsen, 1948 |
| Achaetogeron fisheri Larsen, 1948 |
| Achaetogeron forreri Greene, 1888 |
| Achaetogeron galeottii A. Gray, 1881 |
| Achaetogeron griseus Greenm., 1905 |
| Achaetogeron linearifolius S. Watson, 1891 |