Tilia americana

Lop-sided heart-shaped leaves with saw-toothed edges help identify American basswood tree. Barely emerging in picture: flowers that dangle from papery, surfboard-shaped structures. When mature, dangling little brown balls (the fruit) "hang-glide" to the ground, twirling as they go.
Photographer: Flickr user .Bambo.
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ID tip: Don't confuse this tree's leaves with red or white mulberry (Morus spp.). The margins of basswood are sharply saw-toothed/jagged, but the margins of mulberry are tightly scalloped/rounded. Besides, if you look hard enough on a mulberry tree you'll find a few irregularly shaped leaves (with extra tips, sort of like sassafras), but not on basswood.