Achillea ptarmica

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.

Phenology: Flowering late Jun–mid Sep.
Habitat: Roadsides, disturbed sites, open fields and pastures, in sandy or gravelly soils or in moist to drying silty soils
Elevation: 0–2400 m

Introduced; Greenland, Alta., Man., N.B., Nfld. and Labr. (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

Discussion

Achillea ptarmica is naturalized from Eurasia. “Double-flowered” plants originated as cultivars; apparently, they persist outside of cultivation.

Selected References

None.

Lower Taxa