Family Compositae or Asteraceae (Composite Family).
A rayless Composite: that is, a flower head with only disc flowers and no rays, like a daisy with no “petals.” The yellow button-like discs and lacy fernlike foliage are distinctive. Tansy came over here as a garden staple, but it has made itself at home. It is never abundant enough in Pittsburgh to qualify as a pest; it is only a pleasant visitor popping up in unexpected places, like here along the sidewalk in the central business district of Beechview.
Gray describes the genus and the species:
TANACÈTUM L. TANSY. Heads many-flowered, nearly discoid; flowers all fertile, the marginal chiefly pistillate and 3-5- toothed. Involucre imbricated, dry. Receptacle convex, naked. Achenes angled or ribbed, with a large flat top; pappus a short crown.—Bitter and acrid mostly strong-scented herbs (ours perennial) , with 1-3 pinnately dissected leaves, and corymbed (rarely single) heads. Flowers yellow, in summer. (Name of uncertain derivation.)
T. vulgàre L. (Common T.) Stem 0.5-1 m. high, smooth; leaflets and the wings of the petiole cut-toothed; corymb dense; pistillate flowers terete, with oblique 3-toothed limb; pappus 5-lobed. —Escaped from gardens to roadsides, etc. (Introd. from Eu.) Var. críspum DC. Leaves more cut and crisped.—Frequent in similar places. (Introd. from Eu.)