I can't really see the flower heads but could it be boneset (Eupatorium perfoliatum) ?

Here is a link that might be useful: boneset

Thinking Eupatorium serotinum (Late Boneset) is possible, because that has leaves with fairly long petioles.

Don't mean to hijack but I'm trying to get the Eupatoriums figured out....Jekeesl, would it be correct to assume the E. serotinum flowers later in the season than E. perfoliatum, or is there significant overlap in flowering times and would another difference be in leaf shape? Maybe narrower, dentate leaves for E. serotinum? Thanks!

E. serotinum and E. perfoliatum flowering times can overlap, but E. serotinum is usually a couple of weeks later here. E. serotinum has mid-stem leaves that are opposite, and clearly petiolate. E. perfoliatum has sessile leaves, and the larger ones are cupped.

Jekeesl, thanks so much for your help...I will be looking out for petiolate vs. sessile leaves...even I can manage that one :)!

Looking at the leaves it looks like serotinum to me as well. Just starting to flower in my yard, I don't know why it has the nickname of "late."

Eupatorium serotinum flowers much later than other Eupatorium species in Florida, hence the common name lateflowering thoroughwort I suppose. I read once where the name "thoroughwort" came about because many species flower along thoroughfares. The term "wort" is an old English term for "plant."

Personally, I think it is named "Late Boneset" because it is so slow to develop. The first time I found this species, years ago, the plants were already tall in April. I kept checking on them through May, June, July, and they just sat there. They finally flowered in September. Most plants have the good manners to flower, shortly following a growth spurt. E. serotinum seems retarded to me :).

Good theory jekeesl. Regardless it is a plant much loved by butterflies at the time when they could use a nectar boost.