Hemlock (see Remarks), pruche [Canadian French] (Taylor 1993), ツガ属 (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. T. canadensis and T. heterophylla were discovered early (before 1800) and until 1855 were simply treated as species of Pinus, but in 1842 T. sieboldii, the southern Japanese hemlock, was described as Abies tsugae. In 1847 Endlicher transferred it into Pinus sect. Tsugae, and then in 1855 Carriere gave us the modern name for the genus.
My friend Michael Frankis (M.P. Frankis, e-mail 1999.02.07) has advised me that the common English name "hemlock" refers to the percieved similarity in the smell of the crushed foliage of T. canadensis to that of the poisonous umbelliferous herb, water hemlock Conium maculatum. The two plants are of course totally unrelated, and Tsuga is not poisonous. I have tested this supposition in my back yard, where I have growing both Tsuga heterophylla and Conium maculatum. My plants do indeed resemble each other in odor, apart from a distinct resinous element in the scent of the Tsuga. I don't know for certain that this resemblance, observed in two plants native to western Washington, remains true in eastern North America or in Britain, but it seems plausible. The Conium leaf, by the way, resembles that of certain Cupressaceae in form (especially Thujopsis), a fact noted by Charles F. Partington in The British Cyclopedia of 1836, who says that the "hemlock spruce" is "so called from its branches in tenuity and position resembling the foliage of the common hemlock." André (1964) also asserted a resemblance between the foliage of Conium and that of the conifer, and that this was the reason the genus name name Conium was applied to poison hemlock. So there are several convergences between conifers and this flowering plant.
We now turn to Roman times, when the plant we now call Picea abies was known simply as Picea, because it was such a common tree in the land of Picea, which we now call Prussia. The common name "spruce" is also derived from the word "Prussia", as is the French name of hemlock, "pruche." But when did they start to give that name to the hemlock?
The first hemlock known to western science was T. canadensis, which would have been encountered by European immigrants to what is now maritime Canada and New England, places where this tree grows near the sea. It is thus likely that doctors or apothecaries, who would have been interested in the medicinal uses of the foliage of both plants, here first noted the resemblance in odor between Tsuga and Conium, and gave the plant its common name. Soon, though, it came to the attention of botanists. Linnaeus in 1763 acknowledged the existence of the species with the name Pinus canadensis, but it is likely that it was known to the botanical world much earlier (by the mid-1600s its presence in the New World would have been noted) and began to be known as "hemlock spruce", a fine example of an English binomial: the adjective (today we might say "epithet") "hemlock" modifying the generic noun "spruce." This gives a clue to the origin of both its French and English names. Speaking only of conifers (not angiosperms), the French domains in the New World were dominated by conifers of the genus Picea, with abundant P. rubens, P. glauca and P. mariana across the landscape. The English domains, on the other hand, were dominated by various species of Pinus. So the common name "hemlock spruce" suggests a northern origin for the term "hemlock", perhaps French, migrating thence to the English. At any rate, the name "hemlock spruce" was in wide use by the time Menzies used it to describe the new western hemlock (Tsuga heterophylla) he found in 1792, although the genus Picea would not be formally described for another 32 years, and the segregation of Tsuga would not occur for an additional 31 years.
André, Jacques. 1964. La résine et la poix dans l'antiquité, technique et terminologie. L'antiquité classique 33(1):86-97.
Last Modified 2015-06-16