| Achillea ageratum | Mace, Sweet-nancy | Asteraceae | A. decolorans. Schrad. A. serrata. | 2 | 0 |
| Achillea erba-rotta moschata | Musk Milfoil | Asteraceae | A. moschata. | 0 | 2 |
| Achillea millefolium | Yarrow, Boreal yarrow, California yarrow, Giant yarrow, Coast yarrow, Western yarrow, Pacific yarrow | Asteraceae | Achillea lanulosa Nutt. Achillea gracilis Raf. Achillea albida Willd. | 3 | 4 |
| Achillea ptarmica | Sneeze-Wort, Sneezeweed | Asteraceae | | 2 | 1 |
| Achillea santolina | | Asteraceae | | 0 | 1 |
| Achillea sibirica | Siberian Yarrow | Asteraceae | A. alpina. L. A. mongolica. Fisch. | 1 | 1 |
| Acmella oleracea | Toothache plant, Paracress | Asteraceae | Anacyclus pyrethraria (L.) Spreng. Bidens acmelloides Berg. Bidens fervida Lam. Bidens fixa Hook.f. Bidens fusca Lam. Bidens oleracea (L.) Cav. ex Steud. Cotula pyrethraria L. Pyrethrum spilanthus Medik. Spilanthes acmella var. oleracea (L.) C.B.Clarke. Spilanthes acmella var. oleracea (L.) C.B.Clarke ex Hook.f. Spilanthes fusca hort.par. ex Lam. Spilanthes oleracea L. [Illegitimate] Spilanthes oleracea var. fusca (Lam.) DC. Spilanthes oleracea var. oleracea. Spilanthes radicans Schrad. ex DC. [Illegitimate]. | 3 | 3 |
| Acourtia microcephala | Sacapellote | Asteraceae | Perezia microcephala. | 0 | 1 |
| Actinea acaulis arizonica | | Asteraceae | | 0 | 0 |
| Ageratina altissima | White Snakeroot, Richweed | Asteraceae | Eupatorium ageratoides. E. rugosum. E. urticaefolium, | 0 | 2 |
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