|Tsuga subsp. var.||Hemlock Spruce|
Tsuga (Template:IPAc-en, from Template:Lang-ja (Template:Lang), the name of Tsuga sieboldii) is a genus of conifers in the family Pinaceae. The common name hemlock is derived from a perceived similarity in the smell of the crushed foliage to that of the unrelated herb poison hemlock; see hemlock for other senses of the word. Unlike the herb, the species of Tsuga are not poisonous. There are between eight and ten species within the genus depending on the authority, with four occurring in North America and four to six in eastern Asia.
They are medium-sized to large evergreen trees, ranging from 10–60(–79) m tall, with a conical to irregular crown, with the latter occurring especially in some of the Asian species. The leading shoots generally droop. The bark is scaly and commonly deeply furrowed, with the colour ranging from grey to brown. The branches stem horizontally from the trunk and are usually arranged in flattened sprays that bend downward towards their tips. Short spur shoots, which are present in many gymnosperms, are weakly to moderately developed. The young twigs as well as the distal portions of stem are flexible and often pendent. The stems are rough due to pulvini that persist after the leaves fall. The winter buds are ovoid or globose, usually rounded at the apex and not resinous. The leaves are flattened to slightly angular and range from 5–35 mm long and 1–3 mm broad. They are borne singly and are arranged spirally on the stem; the leaf bases are twisted so the leaves lie flat either side of the stem or more rarely radially. Towards the base the leaves narrow abruptly to a petiole set on a forward-angled, pulvinus. The petiole is twisted at the base so that it is almost parallel with the stem. The leaf apex is either notched, rounded, or acute. The undersides have two white stomatal bands (in T. mertensiana they are inconspicuous) separated by an elevated midvein. The upper surface of the leaves lack stomata, except in T. mertensiana. They have one resin canal that is present beneath the single vascular bundle.
The pollen cones grow solitary from lateral buds. They are 3–5(–10) mm long, ovoid, globose, or ellipsoid, and yellowish-white to pale purple, and borne on a short peduncle. The pollen itself has a saccate, ring-like structure at its distal pole, and rarely this structure can be more or less doubly saccate. The seed cones are borne on year-old twigs and are small ovoid-globose or oblong-cylindric, ranging from 15–40 mm long, except in T. mertensiana, where they are cylindrical and longer, 35–80 mm in length; they are solitary, terminal or rarely lateral, pendulous, and are sessile or on a short peduncle up to 4 mm long. Maturation occurs in 5–8 months, and the seeds are shed shortly thereafter; the cones are shed soon after seed release or up to a year or two later. The seed scales are thin, leathery and persistent. They vary in shape and lack an apophysis and an umbo. The bracts are included and small. The seeds are small, from 2 to 4 mm long, and winged, with the wing being 8 to 12 mm in length. They also contain small adaxial resin vesicles. Seed germination is epigeal; the seedlings have four to six cotyledons.
|Standard Cyclopedia of Horticulture|
Tsuga (its Japanese name). Pinaceae. Hemlock Spruce. Hemlock. Ornamental trees, grown chiefly for their graceful habit and handsome evergreen foliage.
Resinous trees with slender horizontal branches: lvs. usually 2-ranked, short-petioled, linear, flat or angular, falling away in drying: staminate aments axillary, sub-globose; ovule-bearing aments terminal, the scales about as long as the bracts, each with 2 ovules at the base: cones small, ovate, or oblong with thin flexible persistent scales, much longer than the bracts; seeds winged.—Nine or 10 species in N. Amer., E. Asia, and the Himalayas. The genus is closely allied to Abies and Picea and differs little in the structure of the fls.; the cones are very similar to those of the larch, but the lvs., which are much like those of Abies in their outward appearance, though smaller, are very different in their internal structure from all allied genera, having a solitary resin-duct situated in the middle of the lf. below the fibro-vascular bundle. The light, soft, brittle and coarse-grained wood is not durable and not much valued except that of T. heterophylla, which is harder and more durable, and that of T. Sieboldii, which is esteemed in Japan for its durability. The bark is rich in tannin and that of T. canadensis is extensively used for tanning leather. T. canadensis should be called "hemlock spruce," but in common speech it is usually alluded to as "hemlock." The "hemlock" of the ancients is a poisonous umbelliferous herb described in this work as Conium maculatum.
The hemlock spruces are evergreen trees of pyramidal habit, with spreading irregularly whorled much ramified branches clothed with small linear usually two-ranked leaves and small cones which are usually freely produced. The cones are only about 1 inch long except in one species, which has cones two or three times as large. T. canadensis is quite hardy North and the Japanese species and T. caroliniana have proved hardy as far north as Ontario. T. Mertensiana is almost as hardy. T. heterophylla is tenderer. There are probably no more beautiful hardy conifers than the hemlocks, and they must be ranked among the most ornamental and useful trees for park planting. They do not have the stiff formal appearance of many of the conifers, but are graceful and stately at the same time. T. heterophylla is the most vigorous species and is more graceful than the Canadian hemlock, but tenderer. T. Mertensiana is noticeable for its light bluish green foliage and the more narrow pyramidal habit. T. Sieboldii is a very handsome species with dark green glossy foliage, but of slow growth and in cultivation usually remains shrubby. T. canadensis bears pruning well and is well suited for tall hedges. The other species will probably bear pruning equally well. The hemlocks are not very particular as to the soil, provided it contains a sufficient amount of constant moisture. Tsugas are not difficult to transplant. Propagation is by seeds sown in spring and by grafting on T. canadensis. The varieties and the Japanese species are also raised from cuttings. See also Arboriculture, Abies, and Picea for cultivation.
T. chinensis, Pritz. Tree, to 120 ft.: branchlets yellowish gray, pubescent: lvs. 1/2 - 1 in. long, rounded or emarginate at the apex, green or nearly so beneath, entire, on young plants sparingly toothed and with narrow white lines beneath: cones sessile, about 1 in. long, lustrous. Cent. and W. China. G.C. III. 39:236 (cones, as T. yunnanensis). Has proved hardy at the Arnold Arboretum and thrives well.—T. dumosa, Sarg. (T. Brunoniana, Carr.). Tree, to 120 ft.: lvs. gradually tapering from the base, serrulate, acutish, with broad silvery white lines beneath, 3/4 – 1 1/4 in. long: cone 1 in. long. Himalayas. Tender.—T. Fretzii - Pseudotsuga taxifolia var. Fretzii.—T. yunnanensis, Mast. Tree, to 150 ft.: branchlets with rufous-gray pubescence: lvs. rounded at the apex, entire, with white lines beneath, 1/2 - 1 in. long: cones 3/4 - 1 in. long, dull, with fewer scales than T. chinensis. W. China. GGrowing at the Arnold Arboretum, and apparently quite hardy. CH
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- Subgenus Tsuga
Tsuga canadensis Eastern Hemlock
Tsuga caroliniana Carolina Hemlock
Tsuga chinensis Taiwan Hemlock
Tsuga diversifolia Northern Japanese Hemlock
Tsuga dumosa Himalayan Hemlock
Tsuga forrestii Forrest's Hemlock
Tsuga heterophylla Western Hemlock
Tsuga sieboldii Southern Japanese Hemlock
- Subgenus Hesperopeuce (Engelm.) Ueno
Tsuga mertensiana Mountain Hemlock
- Standard Cyclopedia of Horticulture, by L. H. Bailey, MacMillan Co., 1963
- w:Tsuga. Some of the material on this page may be from Wikipedia, under the Creative Commons license.
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