3. Tanacetum vulgare Linnaeus, Sp. Pl. 2: 844. 1753.
Common tansy, tanaisie vulgaire
Perennials, mostly 40–150 cm. Stems 1–2+ (ridged), erect, branched distally (glabrous or sparsely hairy). Leaves basal (soon withering) and cauline; petiolate or sessile; blades broadly oblong or oval to elliptic, 4–20 × 2–10 cm, pinnately lobed (rachises ± winged, primary lobes 4–10 pairs, lance-linear to lanceolate or narrowly elliptic, often pinnately lobed or toothed), ultimate margins dentate, faces glabrous or sparsely hairy, gland-dotted. Heads 20–200 in compact, corymbiform arrays. Involucres 5–10 mm diam. Receptacles convex to conic, epaleate. Ray florets 0 (heads disciform, peripheral pistillate florets ca. 20; corollas yellow, lobes 3–4). Disc corollas 2–3 mm. Cypselae 1–2 mm, 4–5-angled or -ribbed, gland-dotted; pappi coroniform, 0.2–0.4 mm. 2n = 18.
Flowering Jul–Sep. Disturbed sites (often moist), abandoned plantings; 10–1600 m; introduced; Alta., B.C., Man., N.B., Nfld. and Labr (Nfld.), N.S., Ont., N.W.T., P.E.I., Que., Sask.; Alaska, Ariz., Ark., Calif., Colo., Conn., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Eurasia; widely introduced in New World and Old World.
Tanacetum vulgare escapes from and/or persists after cultivation. In the flora area, it is naturalized mostly in the northeastern and Pacific Coast states and provinces and sporadically elsewhere.