The American elm (Ulmus americana) and the Siberian elm (Ulmus pumila) are two very different trees. The American elm is a large tree, growing up to 80 feet tall with a trunk diameter of 3-5 feet. It has dark green leaves that are 2-4 inches long and 1-2 inches wide, with double-toothed margins. The Siberian elm is a much smaller tree, only growing 20-40 feet tall with a trunk diameter of 1-2 feet. It has light green leaves that are only 1-2 inches long and 0.5 inches wide, with single-toothed margins. Both trees produce small, round fruits that are 0.25 inches in diameter, but the fruit of the American elm is dark brown while the fruit of the Siberian elm is red.