The galls are small, conical and single-chambered, usually occurring on the lower side of leaves but occasionally on the upper side of leaves and on stems ... When on leaves, the gall is always attached to either a major or minor vein ... Each gall contains a single white larva. Galls on S. rugosa are 2.5–6.0 mm long and 0.7–1.2 mm wide at widest part, tapering toward apex, green to yellowish green, and covered by short, whitish hairs. Very young galls are sometimes accompanied by a tuft of hair at their base, almost as long as the gall itself.

Rhopalomyia clarkei produces a conical leaf gall on Solidago rugosa...these galls, which are abundant in Allegheny County.

Conical, decumbent gall attached to leaf rib...Rhopalomyia clarkeae Felt

Galls are 1–2 mm long, inconspicuous, the same color as the leaf and usually on the underside...