Eastern Cottonwood Populus deltoides
Corrections
The range map published in the Sibley Guide to Trees was made with an older data set and therefore missed some data around the edges of the range, particularly in Florida and the northeast. A replacement map is here:
Thanks for the updated distribution map. The map on the srs.fs.usda page seems to be incorrect and I was trying to find a more accurate distribution of the Eastern Cottonwood.