3. Achillea ptarmica Linnaeus, Sp. Pl. 2: 898. 1753.
Sneezeweed, sneezewort, achillée ptarmique, herbe-à-éternuer
Perennials, 30–60+ cm (rhizomatous). Stems 1, erect, branched distally, proximally glabrate, distally villous or tomentose. Leaves sessile; blades linear to narrowly lanceolate, 3–10 × 3–5 mm, (bases slightly clasping, margins usually serrulate, rarely subentire), faces glabrous or sparsely hairy on midveins adaxially. Heads 3–15+, in simple or compound, corymbiform arrays. Phyllaries 25–30+ in ± 3 series, (light green, midribs yellowish, margins light brown) lanceolate to oblanceolate, faces tomentose. Receptacles flat to slightly convex; paleae oblanceolate, 3–4 mm. Ray florets 8–10(–13), styliferous and sterile (45–70, pistillate, fertile, in horticultural doubles); corollas white, laminae suborbiculate, 4–5 × 4–5 mm (5–7 × 3.5–4.5 mm in doubles). Disc florets 45–75+ (sometimes 0 in doubles); corollas grayish white, ca. 3 mm. Cypselae 1.5–2 mm. 2n = 18.
Flowering late Jun–mid Sep. Roadsides, disturbed sites, open fields and pastures, in sandy or gravelly soils or in moist to drying silty soils; 0–2400 m; introduced; Greenland; Alta., Man., N.B., Nfld. and Labrador (Nfld.), N.S., Ont., P.E.I., Que.; Alaska, Colo., Conn., Idaho, Ind., Maine, Mass., Mich., Minn., Mo., Mont., N.H., N.J., N.Y., N.Dak., Ohio, Pa., R.I., Vt., Wash., W.Va., Wis.; Eurasia.
Achillea ptarmica is naturalized from Eurasia. "Double-flowered" plants originated as cultivars; apparently, they persist outside of cultivation.