Tsuga

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Tsuga
Tsuga heterophylla1.jpg
Tsuga heterophylla
Scientific classification Red Pencil Icon.png
Kingdom: Plantae
Clade: Tracheophytes
(unranked): Gymnospermae
Division: Pinophyta
Class: Pinopsida
Order: Pinales
Family: Pinaceae
Subfamily: Abietoideae
Genus: Tsuga
Carrière
Synonyms [1] [2]
  • MicropeuceGordon, not validly published
  • HesperopeuceLemmon
  • × Tsugo-piceo-tsugaVan Campo & Gaussen
  • × HesperotsugaC.N.Page
  • NothotsugaHu ex C.N.Page.
  • PinusLinnaeus sect. TsugaEndlicher

Tsuga ( /ˈsɡə/ , [3] from Japanese (ツガ), the name of Tsuga sieboldii) is a genus of conifers in the subfamily Abietoideae of Pinaceae, the pine family. The common name hemlock is derived from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant poison hemlock. Unlike the latter, Tsuga species are not poisonous. [4]

Contents

Eight to ten species are within the genus (depending on the authority), with four species occurring in North America and four to six in eastern Asia. [5] [6] [7] [2] [8]

Description

Tsuga diversifolia foliage and cones in snow Tsuga-diversifolia.JPG
Tsuga diversifolia foliage and cones in snow

They are medium-sized to large evergreen trees, ranging from 10–60 m (33–197 ft) tall, with a conical to irregular crown, 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 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. [5] [6] [7] [2] [8]

Tsuga mertensiana foliage and cones MountainHemlock 6739.jpg
Tsuga mertensiana foliage and cones

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. [5] [6] [7] [2] [8]

Taxonomy

Mountain hemlock, T. mertensiana, is unusual in the genus in several respects. The leaves are less flattened and arranged all round the shoot, and have stomata above as well as below, giving the foliage a glaucous color; and the cones are the longest in the genus, 35–80 mm long and cylindrical rather than ovoid. Some botanists treat it in a distinct genus as Hesperopeuce mertensiana (Bong.) Rydb., [9] though it is more generally only considered distinct at the rank of subgenus. [5]

Tsuga canadensis boughs shedding older foliage in autumn Hemlock's deciduous nature.jpg
Tsuga canadensis boughs shedding older foliage in autumn

Another species, bristlecone hemlock, first described as Tsuga longibracteata, is now treated in a distinct genus Nothotsuga ; it differs from Tsuga in the erect (not pendulous) cones with exserted bracts, and male cones clustered in umbels, in these features more closely allied to the genus Keteleeria . [5] [7]

Ecology

The species are all adapted to (and are confined to) relatively moist, cool temperate areas with high rainfall, cool summers, and little or no water stress; they are also adapted to cope with heavy to very heavy winter snowfall and tolerate ice storms better than most other trees. [5] [7] Hemlock trees are more tolerant of heavy shade than other conifers; they are, however, more susceptible to drought. [10]

Threats

The two eastern North American species, T. canadensis and T. caroliniana , are under serious threat by the sap-sucking insect Adelges tsugae (hemlock woolly adelgid). [11] This adelgid, related to the aphids, was introduced accidentally from eastern Asia, where it is only a minor pest. Extensive mortality has occurred, particularly east of the Appalachian Mountains. The Asian species are resistant to this pest, and the two western American hemlocks are moderately resistant. In North America, hemlocks are also attacked by hemlock looper. [12] Larger infected hemlocks have large, relatively high root systems that can bring other trees down if one falls. The foliage of young trees is often browsed by deer, and the seeds are eaten by finches and small rodents.

Old trees are commonly attacked by various fungal disease and decay species, notably Heterobasidion annosum and Armillaria species, which rot the heartwood and eventually leave the tree liable to windthrow, and Rhizina undulata , which may kill groups of trees following minor grass fires that activate growth of the Rhizina spores. [13]

Uses

The wood obtained from hemlocks is important in the timber industry, especially for use as wood pulp. Many species are used in horticulture, and numerous cultivars have been selected for use in gardens. The bark of the hemlock is also used in tanning leather. The needles of the hemlock tree are sometimes used to make a tea and perfume.

Species

Accepted living species [1] [14] [2]
Accepted paleospecies


Formerly included [1]

Moved to other genera: Cathaya Keteleeria Nothotsuga Picea Pseudotsuga Taxus

Related Research Articles

<i>Pseudotsuga</i> Genus of conifers in the family Pinaceae

Pseudotsuga is a genus of evergreen coniferous trees in the family Pinaceae.

Douglas fir Species of tree

The Douglas fir is an evergreen conifer species in the pine family, Pinaceae. It is native to western North America and is also known as Douglas-fir, Douglas spruce, Oregon pine, and Columbian pine. There are three varieties: coast Douglas-fir, Rocky Mountain Douglas-fir and Mexican Douglas fir.

Conifer Division of plants including extinct and current conifers

Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta, also known as Coniferophyta or Coniferae. The division contains a single extant class, Pinopsida. All extant conifers are perennial woody plants with secondary growth. The great majority are trees, though a few are shrubs. Examples include cedars, Douglas-firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, redwoods, spruces, and yews. As of 1998, the division Pinophyta was estimated to contain eight families, 68 genera, and 629 living species.

Pinaceae Family of conifers

The Pinaceae, pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as cedars, firs, hemlocks, larches, pines and spruces. The family is included in the order Pinales, formerly known as Coniferales. Pinaceae are supported as monophyletic by their protein-type sieve cell plastids, pattern of proembryogeny, and lack of bioflavonoids. They are the largest extant conifer family in species diversity, with between 220 and 250 species in 11 genera, and the second-largest in geographical range, found in most of the Northern Hemisphere, with the majority of the species in temperate climates, but ranging from subarctic to tropical. The family often forms the dominant component of boreal, coastal, and montane forests. One species, Pinus merkusii, grows just south of the equator in Southeast Asia. Major centres of diversity are found in the mountains of southwest China, Mexico, central Japan, and California.

<i>Cedrus deodara</i> Species of plant

Cedrus deodara, the deodar cedar, Himalayan cedar, or deodar, is a species of cedar native to the western Himalayas. It grows at altitudes of 1,500–3,200 m (5,000–10,000 ft).

<i>Tsuga canadensis</i> Species of conifer

Tsuga canadensis, also known as eastern hemlock, eastern hemlock-spruce, or Canadian hemlock, and in the French-speaking regions of Canada as pruche du Canada, is a coniferous tree native to eastern North America. It is the state tree of Pennsylvania.

<i>Tsuga heterophylla</i> Species of conifer

Tsuga heterophylla, the western hemlock or western hemlock-spruce, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Sonoma County, California.

<i>Tsuga mertensiana</i> Species of tree found in western North America

Tsuga mertensiana, known as mountain hemlock, is a species of hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern Tulare County, California. Mertensiana refers to Karl Heinrich Mertens (1796–1830), a German botanist who collected the first specimens as a member of a Russian expedition in 1826–1829.

<i>Nothotsuga</i> Genus of conifers

Nothotsuga is a genus of coniferous trees in the family Pinaceae endemic to China. Nothotsuga contains only one species, Nothotsuga longibracteata, commonly known as the bristlecone hemlock, which is found in southeastern China, in southern Fujian, northern Guangdong, northeast Guangxi, northeast Guizhou, and southwest Hunan.

<i>Keteleeria</i> Genus of conifers

Keteleeria is a genus of three species of coniferous trees in the family Pinaceae first described as a genus in 1866.

<i>Pseudolarix</i> Genus of deciduous conifers in the family Pinaceae

Pseudolarix is a genus of coniferous trees in the pine family Pinaceae containing three species, the extant Pseudolarix amabilis and the extinct species Pseudolarix japonica and Pseudolarix wehrii. Pseudolarix species are commonly known as golden larch, but are not true larches (Larix) being more closely related to Keteleeria, Abies and Cedrus. P. amabilis is native to eastern China, occurring in small areas in the mountains of southern Anhui, Zhejiang, Fujian, Jiangxi, Hunan, Hubei and eastern Sichuan, at altitudes of 100–1,500 m (328–4,921 ft). P. wehrii is described from fossils dating to the Early Eocene, Ypresian, of Western North America where it is found in the Eocene Okanagan Highlands Allenby and Klondike Mountain Formations. The youngest known occurrence is of mummified fossils found in the Late Eocene Buchanan Lake Formation on Axel Heiberg Island. P. japonica is known from Middle Miocene to Pliocene sediments in Japan and Miocene deposits of Korea. Fossils assigned to Pseudolarix as a genus date possibly as old as the Early Cretaceous Hauterivian stage in Mongolia.

Fraser fir Species of conifer

The Fraser fir is a species of fir native to the Appalachian Mountains of the Southeastern United States.

<i>Tsuga caroliniana</i> Species of conifer

Tsuga caroliniana, the Carolina hemlock, is a species of Tsuga, native to the Appalachian Mountains in southwest Virginia, western North Carolina, extreme northeast Georgia, northwest South Carolina, and eastern Tennessee. Its habitat is on rocky mountain slopes at elevations of 700–1,200 m (2,300–3,900 ft). The optimal growing condition is a partly shady area with moist but well-drained soil in a cool climate.

<i>Keteleeria davidiana</i> Species of conifer

Keteleeria davidiana is a coniferous evergreen tree native to Taiwan and southeast China, in the provinces of Gansu, Guangxi, Guizhou, Hubei, Hunan, Shaanxi, Sichuan, and Yunnan. It also occurs in the very northern part of Vietnam. The tree is restricted to hills, mountains, and valleys at elevations of 200–1500 m. Generally, it grows in regions with a more continental climate than the other two Keteleeria species.

Abietoideae Subfamily of the conifer family Pinaceae

Abietoideae is a subfamily of the conifer family Pinaceae. The name is from the genus Abies (firs), which contains most of the species in the genus. Six genera are currently assigned to this subfamily: Abies, Cedrus, Keteleeria, Nothotsuga, Pseudolarix, and Tsuga.

<i>Tsuga sieboldii</i> Species of conifer

Tsuga sieboldii, also called the southern Japanese hemlock, or in Japanese, simply tsuga (栂), is a conifer native to the Japanese islands of Honshū, Kyūshū, Shikoku and Yakushima. In Europe and North America the tree is sometimes used as an ornamental and has been in cultivation since 1861.

<i>Tsuga dumosa</i> Species of conifer

Tsuga dumosa, commonly called the Himalayan hemlock or in Chinese, Yunnan tieshan, is a species of conifer native to the eastern Himalayas. It occurs in parts of Nepal, India, Bhutan, Myanmar, Vietnam and Tibet. Within its native range the tree is used for construction as well as for furniture. In Europe and North America, it is occasionally encountered as an ornamental species and was first brought to the United Kingdom in 1838.

<i>Tsuga chinensis</i> Species of conifer

Tsuga chinensis, commonly referred to as the Taiwan or Chinese hemlock, or in Chinese as tieshan, is a coniferous tree species native to China, Taiwan, Tibet and Vietnam. The tree is quite variable and has many recognised varieties, though some are also maintained to be separate species by certain authorities. The tree was recently discovered in the mountains of northern Vietnam, making that the southernmost extension of its range.

Laricoideae Subfamily of plants

The Laricoideae are a subfamily of the Pinaceae, a Pinophyta division family. They take their name from the genus Larix (larches), which contains inside most of the species of the group and is one of only two deciduous genera of the pines complex. Ecologically important trees, the Laricoideae form pure or mixed forest associations often dominant in the ecosystems in which they are present, thanks also to their biological adaptations to natural disturbances, to reproductive strategies put in place and high average longevity of the individuals. Currently are assigned to this subfamily three genera and its members can be found only in Northern Hemisphere. The various species live for the most part in temperate or cold climates and are the more northerly conifers; some constitute an important source of timber and non-timber forest products.

References

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  12. USDA Forest Service NA-PR-05-92
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