I just noticed the latest research (and iNat accordingly) has moved S. gigantea out of subsect. Triplinerviae to subsect. Serotinae instead. So now those tricky large goldenrods need to be ID’d up to sect. Unilaterales instead I guess…
Subsect. Serotinae (Rydb.) Semple & Beck included the North American Solidago gigantea Ait. and two South American species S. chilensis Meyen and S. microglossa DC. –– no obvious morphological feature unites these three species.
Frustrating but it least it does seem a bit easier to ID of the 3… I have never learned canadensis/altissima, does this summary seem accurate? The presence of galls and distribution of leaf serrations seem like the easiest features to use if so…
I see Broad-leaved and Bluestem a lot low to the ground in very shaded forests where other goldenrods don’t grow and they’re pretty easy to distinguish from each other. I don’t see Rough-stemmed often enough to recognize them but I just noticed someone left a helpful comment about the veins on one of my observations years ago.
The other species I’ve seen were smaller ones in fens, alvars, or far northern Ontario and I don’t know how to ID any of them.