Baby or Dwarf Goldenrod
Solidago nana Nutt. is native to dry to wet soils, often alkaline meadows and flats, and open wooded slopes of the the Great Basin and western slope of the central Rocky Mts. in the U.S. The species is distinguished by having heads secund, in rounded, secund pseudo-flat-topped pyramidal inflorescences and stems and leaves with dense short soft hairs (Semple & Cook 2006 FNA). It is the only species in S. subsect. Nemorales that can look whitish in the field due to a higher density of short hairs. It shoots develop from a short branching caudex rather the elongated rhizomes. The species is diploid 2n=18.
Solidago nana was included in a multivariate study of S. subsect. Nemorales (Semple et al. 2018) and was separated strongly from the other six species using only four floral characters. A key to the taxa in the subsection was included in the article. Included in the analysis was Baker 722 (COLO) from Pagosa Springs, Archuleta Co., Colorado was placed into S. nana in the classification analysis although it had previously been identified incorrectly as S. rigida (and Oligoneuron rigida); it was the unseen voucher cited for the presence of S. rigida in the Flora of the Four Corners.
Collections labeled as S. nana from the Front Range in Colorado that I have seen were all S. decemflora or S. velutina. This may be true for other collections that are the basis of literature/internet reports indicated on the map below from further east In Colorado. The range appears to be broken up into many disjunction areas.
Solidago nana was included in the polygenomic phylogeny of Solidago and was placed in the S. subg. Nemorales clade with 100% probability (Semple et al. 2023 in press).