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''Tsuga'' (, from
Japanese Japanese may refer to: * Something from or related to Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea ...

Japanese
(), the name of ''
Tsuga sieboldii
Tsuga sieboldii
'') is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...
s in the subfamily Abietoideae of
Pinaceae The Pinaceae, or pine family, are conifer trees or shrubs, including many of the well-known conifers of commercial importance such as Cedrus, cedars, firs, Tsuga, hemlocks, larches, pines and spruces. The family is included in the order Pinales, ...

Pinaceae
, the pine family. The
common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often cont ...
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. The genus comprises eight to ten species (depending on the
authority In the fields of sociology Sociology is a social science that focuses on society, human social behavior, patterns of Interpersonal ties, social relationships, social interaction, and aspects of culture associated with everyday life. It use ...
), with four species occurring in North America and four to six in eastern Asia.


Description

They are medium-sized to large
evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, ...

evergreen
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondar ...

tree
s, ranging from 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
shoot In botany, a plant shoot consists of any plant stem A stem is one of two main structural axes of a vascular plant, the other being the root. It supports leaf, leaves, flowers and fruits, transports water and dissolved substances between the ...

shoot
s, which are present in many
gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...
s, 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 A pulvinus (pl. ''pulvini'') is a joint-like thickening at the base of a plant leaf or leaflet that facilitates growth-independent movement. Pulvini are common, for example, in members of the bean family Fabaceae (Leguminosae) and the prayer plant ...
that persist after the
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

leaves
fall. The winter
bud
bud
s are ovoid or globose, usually rounded at the apex and not resinous. The leaves are flattened to slightly angular and range from long and 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
stoma In botany, a stoma (from Greek language, Greek ''στόμα'', "mouth", plural "stomata"), also called a stomate (plural "stomates"), is a pore found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange. ...

stoma
tal bands (which are inconspicuous on '' T. mertensiana'') separated by an elevated midvein. The upper surface of the leaves lack stomata, except those of ''T. mertensiana''. They have one resin canal that is present beneath the single vascular bundle. The
pollen Pollen is a powdery substance produced by Spermatophyte, seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects ...

pollen
cones grow solitary from lateral buds. They are usually up to in length, 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 A conifer cone (in formal botany, botanical usage: strobilus, plural strobili) is a seed-bearing organ on gymnosperm plants. It is usually woody, ovoid to globular, including scales and bracts arranged around a central axis, especially in con ...
are borne on year-old twigs and are small ovoid-globose or oblong-cylindric, ranging from long, except in ''T. mertensiana'', where they are cylindrical and longer, in length; they are solitary, terminal or rarely lateral, pendulous, and are
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
or on a short peduncle up to long. Maturation occurs in 5–8 months, and the
seed A seed is an Plant embryogenesis, embryonic plant enclosed in a testa (botany), protective outer covering, along with a food reserve. The formation of the seed is a part of the process of reproduction in seed plants, the spermatophytes, includ ...

seed
s 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
bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

bract
s are included and small. The seeds are small, from long, and winged, with the wing being in length. They also contain small adaxial resin vesicles. Seed germination is
epigeal Epigeal, epigean, epigeic and epigeous are biological Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all o ...
; the seedlings have 4–6
cotyledon A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germination, germinating see ...
s.


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, long and cylindrical rather than ovoid. Some botanists treat it in a distinct genus as ''Hesperopeuce mertensiana'' (Bong.) Rydb., though it is more generally only considered distinct at the rank of subgenus. Another species, bristlecone hemlock, first described as ''T. 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''.


Species

; Accepted living species * '''' – eastern hemlock – Eastern Canada, Eastern United States * '' Tsuga caroliniana'' – Carolina hemlock – Southern
Appalachians The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a mountain range, system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovicia ...
* '' Tsuga chinensis'' – Taiwan hemlock – much of China incl Tibet + Taiwan * '''' – northern Japanese hemlock –
Honshu , historically called , is the largest and most populous island of Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the we ...
,
Kyushu is the third-largest island of Japan's Japanese archipelago, five main islands and the most southerly of the four largest islands (i.e. excluding Okinawa Island, Okinawa). In the past, it has been known as , and . The historical regional name ...

Kyushu
* '''' – Himalayan hemlock –
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over list ...

Himalayas
,
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...

Tibet
,
Yunnan Yunnan , () is a landlocked Provinces of China, province in Southwest China, the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is ...

Yunnan
,
Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; Postal romanization, alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestantism in Sichuan, Protestant missions) is a Prov ...

Sichuan
* '' Tsuga forrestii'' – Forrest's hemlock –
Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; Postal romanization, alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestantism in Sichuan, Protestant missions) is a Prov ...

Sichuan
,
Yunnan Yunnan , () is a landlocked Provinces of China, province in Southwest China, the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is ...

Yunnan
,
Guizhou Guizhou (; formerly Kweichow) is a landlocked province in the southwest region of the People's Republic of China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries ...

Guizhou
* ''
Tsuga heterophylla ''Tsuga heterophylla'', the western hemlock or western hemlock-spruce, is a species of Tsuga, hemlock native to the west coast of North America, with its northwestern limit on the Kenai Peninsula, Alaska, and its southeastern limit in northern ...
'' – western hemlock – Western Canada, Northwestern United States * '' Tsuga × jeffreyi'' –
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...
, Washington * ''
Tsuga mertensiana ''Tsuga mertensiana'', known as mountain hemlock, is a species of Tsuga, hemlock native to the west coast of North America, found between Southcentral Alaska and south-central California. Description ''Tsuga mertensiana'' is a large evergreen co ...
'' – mountain hemlock – Alaska,
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost Provinces and territories of Canada, province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include ...
, Western United States * '''' – southern Japanese hemlock – Japan * '' Tsuga ulleungensis'' – Ulleungdo hemlock –
Ulleungdo Ulleungdo (also spelled Ulreungdo; Hangul: , ) is a South Korean island 120 km (75 mi) east of the Korean Peninsula in the Sea of Japan, formerly known as the Dagelet Island or Argonaut Island in Europe. Volcanic in origin, the rocky s ...
island, Korea ;Accepted paleospecies * †'' Tsuga aburaensis'' - Abura, Hokkaido (Miocene) * †'' Tsuga asiatica'' - Lawula Formation,
Tibet Tibet (; ''Böd''; ) is a region in East Asia, covering much of the Tibetan Plateau and spanning about . It is the traditional homeland of the Tibetan people. Also resident on the plateau are some other ethnic groups such as Monpa people, ...

Tibet
(
Priabonian The Priabonian is, in the International Commission on Stratigraphy, ICS's geologic timescale, the latest age (geology), age or the upper stage (stratigraphy), stage of the Eocene epoch (geology), Epoch or series (stratigraphy), Series. It spans ...
) * †'' Tsuga europaea'' -Maria Theresia mine
Aachen Aachen ( ; ; Aachen dialect: ''Oche'' ; French and traditional English: Aix-la-Chapelle; or ''Aquisgranum''; nl, Aken ) is, with around 249,000 inhabitants, the 13th-largest city in North Rhine-Westphalia, and the 28th-largest city of Ge ...
(Miocene) * †'' Tsuga nanfengensis'' -
Yunnan Province Yunnan , () is a landlocked province A province is almost always an administrative division within a country or sovereign state, state. The term derives from the ancient Roman ''Roman province, provincia'', which was the major territoria ...
(Late Miocene) * †'' Tsuga swedaea'' - Buchanan Lake Formation,
Axel Heiberg Island Axel Heiberg Island ( iu, ᐅᒥᖕᒪᑦ ᓄᓈᑦ, ) is an uninhabited island in the Qikiqtaaluk Region The Qikiqtaaluk Region, Qikiqtani Region (Inuktitut syllabics: ᕿᑭᖅᑖᓗᒃ ) or Baffin Region is the easternmost, northernmo ...
(
Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
) * †'' Tsuga taxoides'' - Inner Mongolia (Early Cretaceous) * †'' Tsuga xianfengensis'' -
Yunnan Province Yunnan , () is a landlocked province A province is almost always an administrative division within a country or sovereign state, state. The term derives from the ancient Roman ''Roman province, provincia'', which was the major territoria ...
(late Miocene) ; Formerly included Moved to other genera: '' Cathaya Keteleeria Nothotsuga
Picea A spruce is a tree of the genus ''Picea'' (), a genus of about 35 species of coniferous evergreen trees in the family Pinaceae, found in the northern temperate and boreal ecosystem, boreal (taiga) regions of the Earth. ''Picea'' is the sole gen ...
Pseudotsuga ''Pseudotsuga'' is a genus of evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm cl ...
Taxus ''Taxus'' is a genus of coniferous trees or shrubs known as yews in the family Taxaceae. They are relatively slow-growing and can be very long-lived, and reach heights of , with trunk girth averaging . They have reddish Bark (botany), bark, lance ...
''


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
snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout ...
fall and tolerate
ice storm An ice storm, also known as a glaze event or a silver storm is a type of winter storm A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, Rain and snow ...
s better than most other trees. Hemlock trees are more tolerant of heavy shade than other conifers; they are, however, more susceptible to drought.


Threats

The two eastern North American species, '' T. canadensis'' and '' T. caroliniana'', are under serious threat by the sap-sucking
insect Insects (from Latin ') are pancrustacean Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, Thorax (ins ...
''Adelges tsugae'' (
hemlock woolly adelgid The hemlock woolly adelgid (; ''Adelges tsugae''), or HWA, is an insect of the order Hemiptera (true bugs) native to East Asia. It feeds by sucking sap from hemlock and spruce trees (''Tsuga'' spp.; ''Picea'' spp.). In its native range, HWA ...
). This adelgid, related to the
aphid Aphids are small sap-sucking insects and members of the Taxonomic rank, superfamily Aphidoidea. Common names include greenfly and blackfly, although individuals within a species can vary widely in color. The group includes the fluffy white Erio ...
s, was introduced accidentally from eastern Asia, where it is only a minor pest. Extensive mortality has occurred, particularly east of the
Appalachian Mountains The Appalachian Mountains (french: Appalaches), often called the Appalachians, are a mountain range, system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician ...
. 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.USDA Forest Service NA-PR-05-92 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 Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the ...
, and the seeds are eaten by
finch The true finches are small to medium-sized passerine birds in the family (biology), family Fringillidae. Finches have stout conical bills adapted for eating seeds and nuts and often have colourful plumage. They occupy a great range of habitats w ...
es and small
rodent Rodents (from Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around ...
s. Old trees are commonly attacked by various
fungal A fungus (plural, : fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified ...
disease and decay species, notably '' Heterobasidion annosum'' and ''
Armillaria ''Armillaria'' is a genus of fungi that includes the ''Armillaria mellea, A. mellea'' species known as honey fungi that live on trees and woody shrubs. It includes about 10 species formerly categorized summarily as ''A. mellea''. ''Armill ...
'' 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.Phillips, D. H., & Burdekin, D. A. (1992). ''Diseases of Forest and Ornamental Trees''. Macmillan .


Uses

The wood obtained from hemlocks is important in the timber industry, especially for use as
wood pulp Pulp is a Lignocellulosic biomass, lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibers from wood, fiber crops, Paper recycling, waste paper, or cotton paper, rags. Mixed with water and other chemica ...
. Many species are used in
horticulture Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprouts, mushrooms, algae, flowers, seaweeds and no ...
, and numerous
cultivar A cultivar is a type of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and when Plant propagation, propagated retain those traits. Methods used to propagate cultivars include: division, root and st ...
s 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.


References


External links

* * {{Authority control Conifer genera