Sp. Pl. 2: 896. 1753
Gen. Pl. ed. 5, 382. 1754
Subtropic to temperate and arctic regions of North America and Eurasia.
Species ca. 115 (4 in the flora).
Centers of diversity for Achillea are in Europe and Asia. Achillea ageratum, A. distans, and A. ligustica have been reported as occurring in North America. Labels on herbarium specimens examined indicated that those reports were based on cultivated plants; there is no evidence that any of the three has become established in our flora. Achillea filipendulina may be persistent or established in California (F. Hrusa et al. 2002) and in Michigan (E. Voss 1972–1996, vol. 3).
Achillea includes aromatic herbs with diverse vegetative morphologies. Floral characters show much less variation. Some species are widely cultivated both in Eurasia and North America. Interspecific hybridization has made identifications difficult and has evidently contributed to long lists of synonyms for some species.
Plants of Achillea contain secondary metabolites with purported therapeutic and pharmacologic uses. Native Americans used the plants to treat earaches, diarrhea, and hemorrhages.
|1||Leaf blades 1–2-pinnately lobed (lobes of single leaves often arrayed in multiple planes)||> 2|
|1||Leaf blades not lobed (margins usually serrulate, rarely subentire or serrate to doubly serrate)||> 3|
|2||Phyllaries 20–30 in 3 series; ray florets (3–)5–8, laminae 1.5–3 × 1.5–3 mm; cypselae 1–2 mm||Achillea millefolium|
|2||Phyllaries 10–13 in (1–)2 series; ray florets 8–10(–13), laminae 1–1.5 × 2–2.5 mm; cypselae 0.75–1 mm||Achillea nobilis|
|3||Ray laminae 4–5 mm; disc florets 45–75+; leaf margins usually serrulate, rarely subentire.||Achillea ptarmica|
|3||Ray laminae 1–3 mm; disc florets 25–30+; leaf margins serrate or doubly serrate (teeth antrorse)||Achillea alpina|