Hemlock, pruche [Canadian French] (Taylor 1993), TSUGA [Japanese].
Syn: Pinus Linnaeus sect. Tsuga Endlicher 1847 (Taylor 1993).
Tsuga includes two subgenera, subgen. Hesperopeuce (Lemmon) Ueno (syn. genus Hesperopeuce Lemmon; includes only T. mertensiana), and subgen. Tsuga (includes all other species). The subgenera are distinguished by both cone and foliage characters; see description below and T. mertensiana for details. The eight species in this treatment are:
Another species described as an aberrant member of this genus, T. longibracteata W.C. Cheng, is now treated in a separate genus Nothotsuga, in some respects intermediate between Tsuga and Keteleeria.
Trees: Evergreen with a conic to irregularly ovoid (in some Asian species) crown; leading shoot usually drooping.
Bark: Gray to brown, scaly, often deeply furrowed.
Branches: Horizontal, often arranged in flattened 'sprays' and arched downward.
Shoots: Short (spur) shoots moderately developed; young twigs and distal portions of stem flexuous and pendent, roughened by peglike projections persisting after leaves fall.
Leaves: 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 acute, rounded or notched; stomata in two bands below; upper surface free of stomata except in subgen. Hesperopeuce; resin canals 1. Buds mostly rounded at apex, not resinous. Cotyledons 4-6.
Pollen cones: < 8 mm long, solitary, globose, brown, borne on year-old twigs.
Seed cones: Also borne on year-old twigs, maturing in 5-7 months, shedding seeds and falling soon thereafter or persisting for several years; pendent, ovoid or oblong (oblong-cylindric in subgen. Hesperopeuce), sessile or nearly so.
Cone scales: Persistent, shape various, thin, leathery, glabrous (pubescent in subgen. Hesperopeuce), lacking apophysis and umbo; bracts small, included.
Seeds: Ca. 3-5 × 2-3 mm, with numerous small resin vesicles; winged, with wing thin, 5-10 mm. x=12 (Taylor 1993, M.P. Frankis e-mail 1999.02.07).
Temperate North America and eastern Asia. Species of Tsuga are native to relatively moist climates where water stresses are minimal. Most are conspicuous, if not dominant, members of the communities in which they occur (Taylor 1993).
Probably T. heterophylla.
Probably T. mertensiana.
"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" (Taylor 1993).
The Latin name is from the Japanese name for T. sieboldii. The common English name 'Hemlock' refers to the percieved similarity in the smell of the crushed foliage of the species first known in Britain (T. canadensis) to that of the very poisonous umbelliferous herb water hemlock Conium maculatum. The two plants are of course totally unrelated, and Tsuga is not poisonous (M.P. Frankis, e-mail 1999.02.07).
Last Modified 2012-11-23