The tree designated as the national tree of the United States in 2004 was the oak, representing the genus Quercus.
Congress made the designation official in 2004 through federal law. The wording refers to the oak genus rather than one particular oak species, because North America contains many native species of Quercus. Oaks are widespread across the United States and have long been associated with strength, endurance, shelter, and civic history.
Oaks also support an exceptionally large number of organisms. Their acorns feed wildlife such as squirrels, deer, turkeys, and jays, while mature trees provide habitat for insects, birds, and fungi. Several famous American trees, including the Charter Oak of Connecticut, have acquired historical importance.
A common mix-up is assuming that the United States chose the sequoia because of its size or the maple because of its autumn color. Those trees are culturally important, but the official national tree is the oak. The legal designation is sometimes phrased as “the tree genus Quercus, commonly known as the oak tree.”