Tsuga mertensiana, known as mountain hemlock, is a species of hemlock native to the west coast of North America, found between Southcentral Alaska and south-central California. Description Tsuga mertensiana is a large evergreen conifer growing up to tall, with exceptional specimens as tall as tall. They have a trunk diameter of up to . The bark is about thick and square-cracked or furrowed, and purplish-brown to gray in color. The crown is a neat, slender, conic shape in young trees with a tilted or drooping lead shoot, becoming cylindric in older trees. At all ages, it is distinguished by the slightly pendulous branchlet tips. The shoots are orange–brown, with dense pubescence about long. The leaves are needle-like, long and broad, soft, blunt-tipped, only slightly flattened in cross-section, pale glaucous blue-green above, and with two broad bands of bluish-white stomata below with only a narrow green midrib between the bands; they differ from those of any other species of hemlock in also having stomata on the upper surface, and are arranged spirally all around the shoot. The cones are small (but much longer than those of any other species of hemlock), pendulous, cylindrical, long and broad when closed, opening to broad, superficially somewhat like a small spruce cone. They have thin, flexible scales long. The immature cones are dark purple (rarely green), maturing red–brown 5 to 7 months after pollination. The seeds are red–brown, long, with a slender, -long pale pink–brown wing. Taxonomy There are three taxa, two subspecies and a minor variety: Tsuga mertensiana subsp. mertensiana. Northern mountain hemlock. Central Oregon northwards. Cones smaller, long, broad when open, with 50 to 80 scales. Tsuga mertensiana subsp. mertensiana var. mertensiana. Northern mountain hemlock. Leaves gray-green on both sides. Tsuga mertensiana subsp. mertensiana var. jeffreyi (Henry) Schneider. Jeffrey's mountain hemlock. Mixed with var. mertensiana; rare. Leaves greener, less glaucous above, paler below; cones indistinguishable from the type. At one time it was thought to be a hybrid with western hemlock, but there is no verified evidence for this. Tsuga mertensiana subsp. grandicona Farjon. California mountain hemlock; syn. T. hookeriana (A.Murray) Carrière, T. crassifolia Flous. Central Oregon southwards. Leaves very strongly glaucous. Cones larger, long, broad when open, with 40 to 60 scales. Etymology Mertensiana refers to Karl Heinrich Mertens (1796–1830), a German botanist who collected the first specimens as a member of a Russian expedition in 1826–1829. Distribution The distribution of T.