I've been trying to collect all the locally native Goldenrods. Some are quite easy, such as Solidago graminifolia, the Grass-leaved Goldenrod, but others are totally confusing.
In some cases the plants are so affected by growing conditions that I simply can't tell them apart. Solidago nemorosa, Grey-leaved Goldenrod, is usually quite easy to spot: short, one-sided wand-like flower spikes which nod over to one side, only a few small leaves along the stem, and no rosette of leaves at ground level at the time it blooms. So what the heck came up in the rock garden? The flower stalk was about 20" high, well-branched, with flowers all around each branch, and a healthy rosette of leaves on the ground.The individual flowers matched the description of S. nemorosa in J.C. Semple's Goldenrods of Ontario, but the form of the flower stalk did not. It was in no way wand-like, much more what I'd call a plume. The rosette leaves matched, but should not have been there at the time the plant bloomed. Then there is a plant I brought back from an alvar I visited, which in fact looked exactly like this one except for being 4" high. It was growing in a huge field of Grey-leaved Goldenrods, all of which looked 'normal'. So is it a dwarf Grey-leaved or is it a regular one that got stepped on or chewed by a deer? Does S. nemorosa, when cut back early in the season, produce a plume instead of a wand?
I have a similar problem with a Goldie from Shaw Woods. When I try to key it out I get lost every time. It's not quite S. hispida, Hairy Goldenrod, yet it's not quite S. nemorosa either. It also bloomed very late so is not likely to be a form of S. juncea, Early Goldenrod, although the rosette leaves look a lot like it.
The answer: try to grow them all together in a test bed, so they all get the same conditions, and see how they do. Put a regular Grey-leaved, the dwarfish one, and the one from the rock garden all together and see if they are still different next year.