I've been photographing Eastern Joe-Pye Weed, Eupatorium dubium, for some time now but never had much luck with an ID. Well, after hours of head-scratching over Sunday's goldenrod shoot, I had to abandon the process and get on with a post. I guess that gave me the motivation to figure out Joe-Pye Weed, so that's cool. It's not clear how long it'll take to sort out the goldenrods!
There are a few Joe-Pye species and the E. dubium ID was made on the basis of the domed flower head...
... the purple stem with spots (not easy to see here), and the three main veins in each leaf.
From How To Know The Wildflowers:
"The summer is nearly over when the tall, conspicuous Joe- Pye-weeds begin to tinge with "crushed raspberry" the lowlands through which we pass. In parts of the country it is nearly as common as the golden-rods and asters which appear at about the same season. With the deep purple of the iron-weed it gives variety to the intense hues which herald the coming of autumn.
Joe Pye is said to have been the name of an Indian who cured typhus fever in New England by means of this plant."
Parsons, Frances Theodora. How To Know The Wildflowers. New York, 1898. 270. Web. Google Web Search. 13 Sep 2009.