At my place the Monarchs (a couple weeks ago) were all attracted to a plant I haven't properly identified.
It looks like queen anne's lace--crowns of many tiny, white flowers. We have a few similar-looking species in the region (Ozarks), and it could be any of them.
Maybe worth a shot finding out if you want some other options for them!
I'm not sure if this is the plant you're describing, but in New England, Monarchs are really attracted to Milkweed. The White Swamp [0] variety may be what you're describing.
I do believe I see a lot of that in the understory, where there is a canopy and shade.
In this particular case, though, it was a similar plant that I normally always see in sunny areas. On the edges of my mowed yard, I was seeing a lot of monarchs for a few days.
It looks like queen anne's lace--crowns of many tiny, white flowers. We have a few similar-looking species in the region (Ozarks), and it could be any of them.
Maybe worth a shot finding out if you want some other options for them!