Hemlock

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Hemlock
Hemlock, common name for any of a genus of coniferous trees (see Pine). The genus includes about ten species, four native to temperate North America and the rest to eastern Asia. Hemlocks are tall, straight evergreens with slender branches bearing scattered, two-ranked leaves and pendulous cones.

The eastern hemlock grows in hilly forests in the northeastern United States and eastern Canada. It is a tall tree, usually 18 to 30 m (60 to 100 ft) in height, with light, spreading, delicate foliage. The leaves are dark green with longitudinal white lines on the lower surfaces. The wood of the eastern hemlock is used extensively as construction lumber, and tannins produced by the bark were at one time used for tanning leather. The Carolina hemlock is a somewhat smaller tree, rarely as tall as 21 m (70 ft), that grows in the mountains of Virginia, the Carolinas, and Georgia. The mountain hemlock is another relatively small species, 6 to 27 m (20 to 90 ft) tall, which grows along the Pacific coast from Alaska to California. The western hemlock is the tallest species in the genus, sometimes reaching a height of 61 m (200 ft). It grows along the Pacific coast from southeastern Alaska to central California. Like the eastern hemlock, it is an important softwood timber tree. About 90 percent of the hemlock used for lumber is western hemlock.

Small specimens of eastern and Carolina hemlock are used as ornamental trees. Two Asian species, the Japanese hemlock and Siebold's hemlock, are cultivated in the northern United States. The North American yew, which belongs to an unrelated coniferous genus, is sometimes called ground hemlock. An insect pest called the woolly algenid, a form of aphid, has become a serious threat to hemlocks in some areas of the United States.

Scientific classification: Hemlocks belong to the family Pinaceae. The eastern hemlock is classified as Tsuga canadensis, the Carolina hemlock as Tsuga caroliniana, the mountain hemlock as Tsuga mertensiana, the western hemlock as Tsuga heterophylla, the Japanese hemlock as Tsuga diversifolia, and Siebold's hemlock as Tsuga sieboldi.


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