See how the mature tree has a shape like the club in a suit of cards? The trunk flares out at the base, and the crown of leaves and branches has that clublike wide and somewhat trailing near the bottom, rounded at the top shape.
Basswoods can grow to be rather grand trees; up to 120 feet (40 metres). The leaves have a heart shape, like their cousins the little-leaf linden (Tilia cordata), though as you can imagine are much larger. They’re also very toothy along the margins.
Also like the little leaf linden, basswoods have scented flowers that droop in a whitish cluster or cyme attached to a single elongated white bract. The small, nutlike fruit also suspends from this bract, which helps the fruit travel when it drops from the tree. I call it a wingnut, but have no idea if anyone else does.
When the leaves are off the trees, basswood and other tilias can be recognized by their large, rounded distinctly reddish buds. They remind me of tiny hearts (actual hearts, not the stylized ones).