4. Tsuga heterophylla (Rafinesque) Sargent, Silva. 12: 73, plate 605. 1898.
Western hemlock, pruche de l'ouest
Abies heterophylla Rafinesque, Atlantic J. 1: 119. 1832
Trees to 50m; trunk to 2m diam.; crown narrowly conic. Bark gray-brown, scaly and moderately fissured. Twigs yellow-brown, finely pubescent. Buds ovoid, gray-brown, 2.5--3.5mm. Leaves (5--)10--20(--30)mm, mostly appearing 2-ranked, flattened; abaxial surface glaucous with 2 broad, conspicuous stomatal bands, adaxial surface shiny green (yellow-green); margins minutely dentate. Seed cones ovoid, (1--)1.5--2.5(--3) ´ 1--2.5cm; scales ovate, 8--15 ´ 6--10mm, apex round to pointed. 2 n =24.
Coastal to midmontane forests; 0--1500m; Alta., B.C.; Alaska, Calif., Idaho, Mont., Oreg., Wash.
Tsuga heterophylla is a dominant species over much of its broad distributional range. It has become the most important timber hemlock in North America. The wood is superior to that of other hemlocks for building purposes and it makes excellent pulp for paper production.
Tsuga × jeffreyi (Henry) Henry was described from southwestern British Columbia and western Washington as a hybrid between T . heterophylla and T . mertensiana . Hybridization is rare, if it occurs at all, and it is therefore of little consequence (R.J. Taylor 1972). At the upper elevational limits of its distribution and under stressful conditions, T . heterophylla tends to resemble T . mertensiana , e.g., leaves are less strictly 2-ranked and stomatal bands on the abaxial leaf surfaces are less conspicuous than at lower elevations.
Western hemlock ( Tsuga heterophylla ) is the state tree of Washington.