Has this bloomed in the past, or is this a brand new thing? The only Aster I know that looks like that is Aster cordifolia. It also looks like some of the weedy Campanula like takesimia or punctata. Compare to those and see if your plant seems close to any of them.

Check White Snakeroot, Ageratina altissima. I have it in my Philly back alley and I keep thinking it's an aster too. https://www.google.com/search?q=ageratina+altissima&source=lnms&tbm=isch&sa=X&sqi=2&ved=0ahUKEwjW2sqT0dHUAhXFbz4KHa86A_YQ_AUIBigB&biw=1440&bih=803

I live near you and have this *everywhere.* I think snakeroot looks right.

I do not see the plant as snakeroot. Snakeroot should have opposite leaves and the leaves above appear alternate like an aster.

https://gobotany.newenglandwild.org/species/ageratina/altissima/

Hard to see in that picture. If the leaves are indeed alternate it could be Eurybia divaricata, White Wood Aster?

Thanks, everybody. I've seen Snakeroot and this is not it. Yes, these leaves are definitely alternate. One of the most distinguishing characteristics of the plant is how when new leaves there is one coming in as a single leaf seemingly at the top of the plant, initially curled up like a vertical cone or flag, and then the leaf gradually unfurls.

Thanks, theparsley -- I have a feeling that's it. Most photos on the web emphasize the flower and it's a little hard to see the leaves to compare, but I think that's it. I've seen this plant in my yard for two or three years, and for whatever reason I never bothered to try to identify it when it's in bloom. In August it'll reveal itself more fully. Thank you, everyone.

Hmm, that doesn't look much like white wood aster either. When I've seen an identified specimen of Eurybia diverticata the stems look markedly dark and sort of wiry. But the leaves match pretty well so --- ? Get good pics of those flowers!

Right, after reading the description on Wikipedia ("serpentine stems") I'm not so sure either.

When I retire I'm going to create a web site that helps people identify plants by seedlings and leaves instead of the (admittedly much more reliable) flowers.

I know: good luck with that.

It does go to show how photographs don't always tell you what you need to know. Googling most plants just gets you a zillion close up images of the flower, especially if it's something most known for its flowers. But that doesn't help you ID the plant without flowers. It also doesn't help you understand the overall form of the plant. If it's a garden plant you're looking at and you want to decide whether to grow it, you want to know what its shape is and how it would fit into the space in your garden. Even a pretty good photo of the whole plant probably doesn't distinctly show all its parts. We better not forget how to hand-draw plants because that's often the best way to get a useful image.

Hand-drawing: yes, that's right, that is so fascinating to consider that. Those 19th-century Victorians knew what they were doing (even before the age of smartphones).

Thanks, NHBabs. Heart-leaved Aster or Blue Wood Aster. It's funny: it's one of those things where it's such a common and annoying weed it makes you wonder that this is actually grown as a cultivated plant. Would be interesting to know the history of when it escaped from cultivation and became (presto chango) weedy.

It's a native plant. "Weedy" in this case means it can get along well in human-disturbed environments.

It's a plant I let grow in many areas. I find that as long as I don't let it go to seed, it is fairly easy to control, but I do quite a bit editing of this plant.

Now that the weeds I didn't catch have bloomed, I discovered that I have both Snakeroot and Blue Wood Aster in my yard. I hadn't looked closely and had thought they were the same weed for many years. Thanks for helping me discover their identity.