Moved from Red Goldenrod Aphid.

Uroleucon is a complicated genus. It's one of the largest in the family with over 200 species, and it needs to be revised. The aphidologist who taught me has been studying aphids longer than I’ve been alive, and he always said not to even bother trying to ID Uroleucon because it was a mess. He had studied some, thought two specimens looked very similar and were the same species but after molecular analysis found they were not the same species, and there were others that looked very different but molecular analysis showed they were different species. I don’t agree that absolutely none of them can be identified, I have confidently identified them to species, but with hostplant species and slide mounted specimens. Other aphidologists tend to have the same opinion, which is why none of them have placed U. nigrotuberculatum to species level here on BugGuide, and I never see them doing it on iNat either.

https://influentialpoints.com/Gallery/Uroleucon_aphids.htm
http://www.aphidsonworldsplants.info/C_HOSTS_Seq_Sop.htm#Solidago

Moved from Brown Ambrosia Aphid.

on this related image: