Perhaps white snakeroot/ageratina

Leaves don't match Ageratina. It looks similar to Eupatorium serotinum, but it would help to see it with the flowers open and also see one individual plant to get an idea of its form.

Jay, I think the flowers are open. They only appear as tiny white buds, and that IS one plant. The thing is huge. It's about 4.5 feet tall and 2.5 feet wide. Of course it's behind Russian Sage, and next to a black eyed susan, so you can't see the trunk or stems. It was given to me by a friend who got it from another friend. The friend who gave it to me shovel pruned her's.

Could you try to get a very close shot of an individual bloom so we can at least take a stab at the family? I’m guessing Asteraceae from what I can make out.

Here is a close-up of those blooms. I used a pencil to give you an idea of how tiny they are, even when opened.

Thanks. Jay.

You're welcome