This species superficially resembles members of the Aster genus rather than appearing as a typical Solidago.  The anomalous features of S. ptarmicoides are not taken into account in the key to the Solidago genus in Budd's Flora.  Thus this key requires:

	heads small and numerous, in terminal or axillary clusters; NOT [usually solitary at ends of branches]
	ray florets yellow; NOT [pink, blue, purple, or white]

The above are clearly not true for S. ptarmicoides.  Note that S. ptarmicoides will interbreed with other Solidago species, indicating its membership in that genus.

 

Ptarmicoides: Answers to key questions in Budd's Flora leading to this species.  inflorescence corymbose, with the branches slanting upward, forming a founded or flat-topped inflorescence; NOT [inflorescence a panicle or spike] ray florets white or pale yellow; NOT [ray florets yellow] ray florets large, 5-8 mm long; NOT [ray florets usually less than 5 mm long]

Solidago: Answers to key questions in Budd's Flora (BF) and Flora of Alberta (FOA) leading to this genus.  These do not include the two incorrect answers described above. plants with fibrous roots; NOT with a taproot juice watery; NOT milky leaves alternate or basal; NOT opposite leaves simple; NOT pinnatifid, NOT divided leaves never spinescent involucral bracts in 2 or more series; NOT [in one series, sometimes with a few much shorter outer ones at the base] involucral bracts well imbricated; NOT scarcely imbricated receptacle naked (FOA) flower heads with both tubular and ray florets ligulate flowers pistillate or neuter; NOT perfect stamens united to form a tube around the pistil pappus composed of hairs; NOT scales, NOT bristles, NOT firm awns, NOT a crown, NOT absent, pappus NOT chaffy pappus single, hairs sometimes unequal but not distinctly divided into an inner and outer series of two lengths; NOT [pappus double, hairs of the outer series inconspicuous, distinctly shorter than the inner]