Tsuga, commonly known as hemlock, is a small genus of evergreen trees known for their graceful, pyramidal shape and distinctive drooping, horizontal branches. Hemlocks are used extensively in landscape plantings and are an important component of forests. Four species are native to North America–T. canadensis (Canadian or eastern hemlock), T. caroliniana (Carolina hemlock), T. heterophylla (western hemlock), and T. mertensiana (mountain hemlock). Cultivars offer a range of ornamental options including low growing ground covers, weeping, and upright forms. Potential disease problems include needle blight, cankers, and rusts. The most serious insect threat to native hemlocks in their eastern range is the hemlock woolly adelgid.