O: American Hornbeam
This small tree is a common understory tree in mixed hardwood forests of the eastern United States. It is very tolerant of shady conditions, so it can thrive beneath larger trees in the overstory. Its ridged bark sometimes resembles the contours of a flexed arm, lending its other common name, “musclewood”. Many animals browse the stems, twigs, and seeds of the Hornbeam, though it is not a preferred food source. However, beavers often use Hornbeam wood to construct their dams and lodges.
You can identify a Hornbeam by its unique rippled bark. Its leaves are oval-shaped with serrated edges, and stay on the branches through the fall and winter - they are not evergreen, but remain attached to the tree as brown, dead leaves.