Most of the flat-topped goldenrods, including stiff goldenrod, are segregated to the genus Oligoneuron by many authors. This is a good example of the persistent ambiguity we see in this age of molecular analysis of plant genomes. The data clearly shows the chains of relationships among plants. It can be presented as amazing fishbone diagrams that show progressive lines and branches of relationships. I suppose it is now theoretically possible to list all plants as a sequence, one plant to the next, and one branch to the next. First comes a, then b, then c, then a branch with 1a, then 1b, then 1c, meanwhile the other branch is 2a, then 2b, and 2c . . . It soon becomes bewildering to those of us that aren't computers. Human beings still must make the decisions on where to draw the lines between different groups and progressions, and how to name everything to organize the discussion. Makes me wonder if we will ever know with finality if stiff goldenrod is Oligoneuron or Solidago. Probably not?