Perennials, (20-)30-60(-80) cm. Stems 1-3+ (ridged), erect, branched (usually glabrous proximally, puberulent distally). Leaves mainly cauline; petiolate; blades ovate to rounded-deltate, 4-10+ × 1.5-4 cm, usually 1-2-pinnately lobed (primary lobes 3-5+ pairs, ± ovate), ultimate margins pinnatifid to dentate, faces (at least abaxial) usually puberulent, gland-dotted. Heads 5-20(-30) in corymbiform arrays. Involucres 5-7 mm diam. Ray florets 10-21+ (more in 'doubles'), pistillate, fertile; corollas white, laminae 2-8(-12) mm. Disc corollas ca. 2 mm. Cypselae ± columnar, 1-2 mm, 5-10-ribbed; pappi 0 or coroniform, 0.1-0.2+ mm. 2n = 18. Flowering Jun-Nov. Disturbed sites, urban areas, roadsides, fields, abandoned plantings; 10-1900 m; introduced; B.C., Ont.; Ala., Colo., Conn., Del., Idaho, Ill., Ind., Ky., Maine, Md., Mass., Mich., Miss., Mo., Mont., Nev., N.H., N.J., N.Y., N.C., Ohio, Oreg., Pa., R.I., S.C., Utah, Vt., Wash., W.Va., Wis., Wyo.; Eurasia; n Africa; widely naturalized in New World and Old World. Tanacetum parthenium is widely cultivated throughout North America.