Upland White Aster , White Flat-top Goldenrod , verge d’or faux-ptarmica

Solidago ptarmicoides (Torr. & A. Gray) Boivin is the flat-topped goldenrod with white rays. (syn: S. asteroides Semple). The species is distinguished by its flat-topped inflorescence, white (rarely cream) ray florets, and stiff, glabrous or sparsely hairy linear leaves (Semple & Cook 2006 FNA).  The phyllaries are single veined. It occurs on dry, sandy, usually calcareous soils, cracks in rocks, limestone pavements, rocky outcrops, grassy slopes, prairies over a wide area of of North America from Saskatechewan to Quebec and south to Colorado, Arkansas and Georgia in widely disjunct populations.  The species is diploid 2n=18.

Solidago ptarmicoides range Semple draft

Although long treated as an "aster", Boivin (1972) based his combination on the original invalid name Doellingeria ptarmicoides Nees but cited the valid name Aster ptarmicoides Torr. & A. Gray as well.  Voss (1996) stated that by citing Torrey & A. Gray the Boivin combination is based on the valid name and is thus also valid.  Brouillet & Semple (1981) discussed reasons why the "White Upland Aster" was really the "White Upland Goldenrod". 

All purported hybrids between Solidago and species of asters are in fact hybrids between Solidago ptarmcoides and species of Solidago sect. Ptarmcoidei, e.g. S. ptarmicoides × S. rigida. This makes the genus names ×Asterago and ×Solidaster superfluous and of no value.