Costmary, chrysanthème balsamique

Balsamita major Desfontaines; Pyrethrum balsamita (Linnaeus) Willdenow var. tanacetoides Boissier; Pyrethrum majus (Desfontaines) Tzvelev

Perennials, 30–80(–120) cm. Stems 1, erect, simple or branched (strigose, glabrate). Leaves basal and cauline; petiolate (proximal) or sessile (distal); blades (basal and proximal cauline) mostly elliptic to oblong, 10–20 × 2–8 cm, usually not pinnately lobed (sometimes with 1–4+ lateral lobes near bases), margins ± crenate, faces usually silvery strigose or sericeous (at least when young), glabrescent, ± gland-dotted. Heads (3–)10–60+ in corymbiform arrays. Involucres (3–)5–8(–10) mm diam. (phyllaries 40–60+ in 3–4+ series, tips usually ± dilated). Receptacles flat to convex. Ray florets usually 0 [sometimes 12–15, pistillate, fertile; corollas white, laminae 4–6+ mm]. Disc corollas ca. 2 mm. Cypselae ± columnar, 1.5–2 mm, 5–8-ribbed (with non-mucilaginous glands); pappi coroniform, 0.1–0.4 mm (entire or ± toothed). 2n = 18, 54.

Flowering Aug–Sep. Disturbed sites, abandoned plantings; 0–1800 m; introduced; N.S., Ont., Que., Sask.; Calif., Colo., Conn., Del., Idaho, Ill., Ind., Kans., Maine, Md., Mass., Mich., Mo., Mont., Nev., N.H., N.Y., Ohio, Oreg., Pa., R.I., S.Dak., Utah, Vt., Wash., Wis., Wyo.; Asia.

The illegitimate name Chrysanthemum balsamita (Linnaeus) Baillon (1882), a new combination based on Tanacetum balsamita Linnaeus (1753) and a later homonym of C. balsamita Linnaeus (1763), pertains here.