hemlock, any tree of the genus Tsuga, coniferous evergreens of the family Pinaceae (pine family) native to North America and Asia. The common hemlock of E North America is T. canadensis, an ornamental tree (sometimes cultivated as a hedge) with small cones and short, dark green leaves so arranged as to give the branchlets a flattened appearance. The tree has been highly valued as a source of tanbark but is now seriously reduced in number. Its wood is soft and light. One of the two Western hemlocks ( T. heterophylla, the tallest tree of the genus) has more valuable wood, which is used in construction work. The ground hemlock is a species of yew. The poison hemlock and water hemlock are herbs of the family Umbelliferae (carrot family) of the division Magnoliophyta. True hemlock is classified in the division Pinophyta, class Pinopsida, order Coniferales, family Pinaceae.