Betula uber (Virginia Round-leaf Birch) is a rare species of tree in the birch family. One of the most endangered species of North American trees, it is endemic to Smyth County, in the U.S. state of Virginia. It is part of the temperate broadleaf and mixed forests biome.The tree was first described in 1918 as a variety of Betula lenta, and elevated to species status in 1945. It hybridizes with B. lenta and it has been suggested that it is actually a round-leaved mutant form of that species.