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Hard to tell exactly, but if I had a guess I'd say you're looking at the fruit of a Sycamore tree, Platanus occidentalis. When these get really mature, they're kind of like dandelion heads, where you can just about blow the seeds off the fruit. You'll find these naturally near aquatic systems such as rivers and ponds, but they are often planted as ornamentals.
Lat: 39.92, Long: -75.08
Spotted on Feb 18, 2011 Submitted on Feb 22, 2011