Solidago (Oligoneuron) riddellii: The taxonomists have this one in a tug of war, but I think ultimately the Oligoneurons (of which this is one) have been classified as goldenrods. Along with Riddellii’s goldenrod, S. rigida and S. ptarmicoides are perhaps the most refined of the goldenrods, the former two completely gardenworthy in their own right. One reason I am using them as subjects in my goldenrod breeding project. Working wonderfully with late season grasses, fall Asters and Heleniums, these make 1 ½ wide x 3ft tall clumps. A stand of these in the mid-garden makes a bold and elegant statement in even the most refined garden designs.