Round-leaf Boneset (Eupatorium rotundifolium) - 2016-7-30 Newark, DE

aka Round-leaf Thoroughwort has started blooming

Look also for Late-flowering Boneset/Thoroughwort (Eupatorium serotinum). Opposite leaves are on long petioles. Can grow to be six feet tall.
http://uswildflowers.com/detail.php?SName=Eupatorium%20serotinum

There are several (four?) sub-species of E. rotundifolium:
http://uswildflowers.com/detail.php?SName=Eupatorium%20rotundifolium
see also:
http://efloras.org/florataxon.aspx?flora_id=1&taxon_id=242416533
and
Weakley's Flora PDF