Gigantea:  Answers to key questions in Budd's Flora and Flora of Alberta leading to this species.   plants 5-20 dm tall; NOT 2-4 dm tall stem below the inflorescence glabrous or very sparsely pubescent ; NOT densely pubescent basal leaves SELDOM forming a rosette basal leaves NOT much longer than stem leaves cauline leaves numerous; NOT rather few leaves lanceolate to oval, more than 4 times as long as wide; NOT obovate, NOT oblanceolate to spatulate, NOT 2.5-3 times as long as wide leaves usually serrate; NOT entire leaves 3-nerved (1 pair of lateral nerves fairly prominent); NOT 1-nerved leaves green; NOT grayish green inflorescence pyramidal; NOT more or less cylindrical, NOT narrowly oval branches of inflorescence more or less spreading or arching; NOT slanting upward, NOT ascending along the stem heads panicled with racemose branches; heads NOT racemose; heads NOT in dense cymose clusters with these arranged in a flat-topped or corymb-like inflorescence heads often secund on the branches involucres mostly 3-6 mm  high; NOT 2-3 mm high

 

Solidago: Answers to key questions in Budd's Flora and Flora of Alberta leading to this genus.  fibrous-rooted, NOT tap-rooted juice watery; NOT milky leaves alternate; NOT opposite leaves simple; NOT pinnatifid, NOT divided heads small and numerous, in terminal or axillary clusters; NOT solitary at ends of branches involucral bracts in 2 or more series; NOT in one series; NOT in one series with a few very much shorter outer bracts at base involucral bracts well imbricated; NOT scarcely imbricated receptacle naked; NOT chaffy or bristly flower heads with both tubular and ray florets; NOT all tubular; NOT all ray ray (ligulate) florets either pistillate or neutral; NOT perfect ray florets yellow; NOT blue, NOT purple, NOT white to pink stamens united to form a tube around the pistil pappus simple (bristles sometimes unequal, but not distinctly divided into two lengths); NOT double (outer inconspicuous and very much shorter than the inner) pappus composed of hairs; NOT composed of scales or bristles, NOT chaffy, NOT of firm awns, NOT absent