Tsuga

Trees evergreen; crown conic; leading shoot usually drooping. Bark gray to brown, scaly, often deeply furrowed. Branches horizontal, often tending to be arranged in flattened "sprays" and arched downward; short (spur) shoots absent; young twigs and distal portions of stem flexuous and pendent, roughened by peglike projections persisting after leaves fall. Buds mostly rounded at apex, not resinous. Leaves borne singly, persisting several years, ± 2-ranked or radiating in all directions, flattened to somewhat angular; abruptly narrowed to a petiolelike base, set on peglike projections, these angled, projected forward, sheath absent; apex rounded or notched; resin canals 1. Cones borne on year-old twigs. Pollen cones solitary, globose, brown. Seed cones maturing in 1 year, shedding seeds and falling soon thereafter or persisting for several years, pendent, ovoid, oblong, or oblong-cylindric, sessile or nearly so; scales persistent, shape various, thin, leathery, lacking apophysis and umbo; bracts small, included. Seeds winged; cotyledons 4–6. x =12.

Distribution

Northern Hemisphere.

Discussion

Species of Tsuga are found naturally in areas of relatively moist climates where water stresses are minimal. Most are conspicuous, if not dominant, members of the communities in which they occur.

Hemlock wood is moderately strong and pliable and lacks resin ducts. With the decline of associated species considered superior in commercial value, hemlocks have become important in the timber industry, especially for pulp. Hemlocks are also widely used for horticultural purposes; numerous cultivars have been developed.

Species ca. 10 (4 in the flora).

Selected References

None.

Lower Taxa

Tsuga canadensis, Tsuga caroliniana, Tsuga heterophylla, Tsuga mertensiana

Key

1	Leaves mostly spreading in all directions from twigs, bearing stomates on both surfaces or on abaxial surface only; seed cones ovoid, oblong, or oblong-cylindric, 2.5-6 cm; scales oblong, 8-18 mm.	> 2
1	Leaves mostly appearing 2-ranked, bearing stomates on abaxial surface only; seed cones ovoid, (1-)1.5-2.5(-3) cm; scales ovate to cuneate, 8-15 mm.	> 3
2	Leaves bearing stomates on both surfaces, thicker along midline; seed cones 3-6 cm, half as wide; montane tree of w North America.	Tsuga mertensiana
2	Leaves bearing stomates on abaxial surface only, flat, not notably thicker along midline, but slightly revolute; seed cones 2.5-4 cm, more than half as wide; montane tree of se United States.	Tsuga caroliniana
3	Buds 2.5-3.5 mm; crown narrowly conic; tree of w North America.	Tsuga heterophylla
3	Buds 1.5-2.5 mm; crown broadly conic; tree of e North America.	Tsuga canadensis