| Alchemilla standleyi L.M. Perry, 1929 |
| Alchemilla subalpestris Rose, 1906 |
| Alchemilla velutina S. Watson, 1882 |
| Alchemilla venusta Schltdl. & Cham., 1830 |
| Alchemilla verticillata Fielding & Gardner, 1844 |
| Alchemilla vulcanica Schltdl. & Cham., 1830 |
| Amelanchier Medik., 1789 |
| Amelanchier denticulata (Kunth) K. Koch, 1869 |
| Amelanchier nervosa (Decne.) Standl., 1922 |
| Amelanchier utahensis Koehne, 1890 |
| Amygdaloideae Arn., 1832 |
| Amygdalus L., 1753 |
| Amygdalus communis L., 1753 |
| Amygdalus havardii W. Wight, 1913 |
| Amygdalus minutiflora (Engelm. ex A. Gray) W. Wright, 1913 |
| Amygdalus persica L., 1753 |
| Aphanes L., 1753 |
| Aphanes occidentalis (Nutt.) Rydb., 1908 |
| Aphanes orbiculata (Ruiz & Pav.) Pers., 1805 |
| Argentina Hill, 1756 |