2. Achillea ptarmica L. (sneezewort, sneezeweed)

Map 938

Plants with short to often relatively long rhizomes. Stems 20–70 cm long, sometimes with short, leafy branches in the leaf axils (these often appearing as fascicles of leaves), sparsely to densely pubescent with white, woolly to cobwebby hairs, sometimes nearly glabrous toward the base at maturity. Leaves sessile. Leaf blades 1–10 cm long, linear to narrowly lanceolate, unlobed, sharply pointed at the tip, the margins sharply but minutely toothed or rarely nearly entire, glabrous or sparsely to moderately pubescent with short, straight to incurved hairs, the venation of 1 raised midvein and also usually 1 or 2 pairs of nearly parallel, somewhat thinner main veins. Inflorescences usually relatively flat-topped. Involucre 4–5 mm long, broadly cup-shaped to hemispherical. Receptacle slightly to moderately convex. Ray florets 8–10(–12) (or more in doubled forms), the corolla 3–5 mm long (to 7 mm in doubled forms), sometimes appearing pebbled or roughened, occasionally with minute, impressed, yellow glands, white. Disc florets perfect, numerous (or few in doubled forms), the corolla 2.5–4.0 mm long, usually with sparse, minute, impressed, yellow glands, white to grayish white. 2n=18. June–September.

Introduced, known thus far only from a historical collection from Phelps County (native of Europe, Asia; introduced widely but sporadically in the northern U.S. and Canada). Roadsides.

This species is cultivated as an ornamental and several cultivars exist, including forms in which most of the disc florets have been transformed into rays. Gleason and Cronquist (1991) and some earlier authors included Missouri in the range of A. ptarmica, but Steyermark (1963) excluded it from the Missouri flora, based upon his finding that historical specimens collected in the city of St. Louis by Earl Sherff originated from cultivated rather than escaped plants. Thus, the species is not mapped from the St. Louis area, but a specimen collected by John Kellogg that was overlooked by Steyermark from a roadside near Rolla justifies the inclusion of A. ptarmica in the flora.