Tsuga heterophylla

Western hemlock is a large evergreen conifer growing to tall, exceptionally , and with a trunk diameter of up to . It is the largest species of hemlock, with the next largest (T. mertensiana or mountain hemlock) reaching a maximum height of . Western hemlock's bark is brown, thin, and furrowed (outwardly appearing similar to that of Douglas-fir). The crown is a very neat broad conic shape in young trees with a strongly drooping lead shoot, and becomes cylindrical in older trees, which may have no branches in the lowest . At all ages, it is readily distinguished by the pendulous branchlet tips. The shoots are very pale buff-brown, almost white, with pale pubescence about long. The leaves are needle-like, long and broad, strongly flattened in cross-section, with a finely serrated margin and a bluntly acute apex. They are mid to dark green above; the underside has two distinctive white bands of stomata with only a narrow green midrib between the bands. They are arranged spirally on the shoots but are twisted at the base to lie in two ranks on either side of the shoot. The cones appear on trees over about 25 years old; Initial growth is slow; one-year-old seedlings are commonly only tall, and two-year-old seedlings tall. Once established, saplings in full light may have an average growth rate of (rarely ) annually until they are tall, and in good conditions still annually when tall. The tallest specimen, tall, is in Prairie Creek Redwoods State Park, California. The species is long-lived, especially at higher elevations, with trees over 1,200 years old known. {{gallery|mode=packed == Etymology ==

The Latin heterophylla in the species name means 'variable leaved'. == Distribution and habitat ==

Tsuga heterophylla is native to the northwest coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California. The species is closely associated with temperate rainforests, and most of its range is less than from the Pacific Ocean. Valleys it can be found in usually receive at least of rain annually. It mostly grows at low altitudes, from sea level to . In western Washington, it can be found up to elevations of . The species can also be found in humid areas of mountains further inland, where western white pine is normally dominant. For example, in the Columbia Mountains in and around southeastern British Columbia and northern Idaho, it grows up to , particularly on north-facing slopes. In the interior part of its range in Idaho, it can be found up to . It has naturalised in some parts of Great Britain and New Zealand—not so extensively as to be considered an invasive species, but as an introduced one. == Ecology ==

Western hemlock is a very shade-tolerant tree; among associated species in the Pacific Northwest, it is matched or exceeded in shade tolerance only by Pacific yew and Pacific silver fir. Older forests are damaged by rot-causing fungi, dwarf mistletoe, and leaf-consuming insects such as Acleris gloverana and Lambdina fiscellaria. ==Cultivation==

Western hemlock is cultivated as an ornamental tree in gardens in its native habitats and along the U.S. Pacific Coast, where its best reliability is seen in wetter regions. In relatively dry areas, as at Victoria, British Columbia, it is exacting about soil conditions. It needs a high level of organic matter (well-rotted wood from an old log or stump is best; animal manures may have too much nitrogen and salt), in a moist, acidic soil. It is also cultivated in temperate regions worldwide. It has gained the Royal Horticultural Society's Award of Garden Merit. It can also be found in large gardens in northwest Europe and southern New Zealand. == Uses ==

Food and medicine The edible cambium can be collected by scraping slabs of removed bark. The resulting shavings can be eaten immediately, or can be dried and pressed into bread, as was done by the natives of Southeast Alaska. The inner bark was eaten by some Native American tribes as an emergency food, and the bark was cooked to make medicinal extracts for tuberculosis, rheumatic fever, and hemorrhage. has been used traditionally in the Northwest Coast. Other uses The bark has long served as a source of tannin for tanning leather. Its fiber is used to make rayon and various plastics. ==In culture==

Western hemlock is the state tree of Washington. ==References==