Herbs perennial; rhizomatous, rarely taprooted when young.
Stems usually 1, usually unbranched, rarely well branched from above middle, sometimes several in a cluster from short, basal rhizomes, setose-villous, leafy throughout.
Basal leaves densely pinnately divided into numerous lobes from a narrow rachis, lobes linear, margins entire or few-toothed or lobed, tips acute; petiolate.
Cauline leaves gradually reduced distally, bases auriculate-clasping, surfaces sparsely to densely setose-villous; short-petiolate or sessile.
Inflorescences terminal, usually flat-topped clusters.
Heads radiate, numerous, small; short-pedunculate.
Involucres cylindrical or narrowly campanulate.
Phyllaries in 3–5 unequal series, erect in flower and fruit, broadly to narrowly lance-ovate, plane or slightly boat-shaped, colorless or with green midribs or tips, midribs distinct, sometimes keeled, surfaces sparsely to densely setose-villous; outer gradually shorter.
Receptacles flat or rounded; paleae membranous.
Ray florets pistillate; rays broad, well exceeding involucres.
Disc florets bisexual; corollas cylindric, enlarged distally, lobes 5, triangular, recurved at anthesis; stamens 5, exserted from corolla; stigmas exserted from stamen tubes.
Fruits oblong, flattened, 2 lateral veins prominent, ± winged; pappi 0.
Asia, Europe, North America. 75–130 species; 1 species treated in Flora.
Achillea filipendulina and A. ptarmica have been reported to have escaped in Oregon but are not yet established.
as described under Achillea
Perennials [subshrubs], 6-80 cm (usually rhizomatous, sometimes fibrous rooted or taprooted; usually aromatic). Stems 1(-4+, clustered), usually erect, branched mostly distally, glabrous or sparsely to densely lanate (hairs usually basifixed). Leaves basal (often withering before flowering) and cauline; alternate; petiolate or sessile (bases ± clasping); blades (cauline equaling basal or slightly smaller distally) linear to oblong-lanceolate, usually 1-2[-4]-pinnately lobed, ultimate margins entire, abaxial faces sparsely to densely lanate, adaxial faces glabrate to sparsely tomentose. Heads radiate [discoid], in compact to open (± flat-topped), simple or compound, corymbiform arrays [borne singly]. Involucres campanulate to hemispheric, mostly 2-3(-5+) mm diam. Phyllaries persistent, 10-30 in (1-)2-3(-4) series, oblong, ovate, or oblanceolate to lanceolate (midribs conspicuous), unequal, margins and apices (pale to black) scarious. Receptacles usually flat to slightly convex, rarely conic, paleate; paleae membranous, ± folded (sometimes each with central resin duct). Ray florets [0] 3-5(-12+), usually pistillate and fertile; corollas usually white (laminae yellow at bases), sometimes pale yellow to pink or purple (tubes ± flattened), laminae orbiculate to suborbiculate (becoming reflexed). Disc florets usually (5-)15-75+, rarely 0, bisexual, fertile; corollas white to grayish or yellowish [yellow, pink], tubes ± flattened (bases ± saccate, clasping apices of cypselae), throats ± campanulate, lobes 5, ± deltate. Cypselae obcompressed, oblong to obovate (margins sometimes winged, apices rounded); ribs usually 2, lateral (sometimes plus 1 adaxial), faces glabrous (pericarps with myxogenic cells, sometimes with resin sacs; embryo sac development monosporic). x = 9.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.