Segregating S. speciosa into some of its component varieties/subspecies (now elevated to species), following POWO.

See discussion here:
https://www.inaturalist.org/flags/501223

Key to Identification from Semple, J.C., L. Tong, and Y.A. Chong. 2017. Multivariate studies of Solidago subsect. Squarrosae. I. The Solidago speciosa complex (Asteraceae: Astereae). Phytoneuron 2017-18: 1–23.

.1. Arrays of heads either narrowly thyrsiform and often interrupted or branches well-spaced; mid cauline leaves 5–20 mm wide; Massachusetts to southern Indiana, south to Georgia and Mississippi, mostly avoiding coastal plain southward ................................................................................. Solidago erecta

.1. Arrays of head broadly thyrsiform or if narrow then congested; mid cauline leaves 3-38 mm wide; Maine to Georgia west to northwestern Ontario and adjacent Manitoba, southwest to Wyoming to New Mexico and south to Georgia in the east and eastern Texas in the west

.2. Basal rosette and lower stem leaves with narrow petioles often making up half or more of the total leaf length, present at flowering; northern Michigan to southeastern Manitoba south to eastern Iowa and northwestern Missouri and adjacent Nebraska ................................ Solidago jejunifolia

.2. Basal rosette and lower stem leaves with narrow petioles making up less than a third of the total leaf length

.3. Lowest stem leaves absent at flowering, present early to mid growing season; middle and upper stem leaves relatively numerous and overlapping ....................Solidago rigidiuscula

.3. Lower stem leaves usually present at flowering, blades tapering to short narrow petioles

.4. Fruit body with some short hairs occurring on the upper half or over much of the fruit; Northwestern Ontario, Black Hills of South Dakota and Wyoming, stems 32–86 cm averaging 58 cm; foot hills of the Rocky Mountains in southern Wyoming to northern New Mexico ...................................................................... Solidago pallida

.4. Fruit body hairless (except for plants from southeastern Maine); stems 65.3–215 cm averaging > 100 cm; eastern US from southeastern Maine south to Georgia west to southeastern Minnesota south to Arkansas ..................................... Solidago speciosa (sensu stricto)