Editing Tsuga

{{Short description|Genus of conifers}}
{{About|the genus}}
{{Automatic taxobox
| taxon = Tsuga
| authority = ([[Stephan Endlicher|Endl.]]) [[Elie-Abel Carrière|Carrière]]
| synonyms_ref = <ref name=WCSP/><ref name="FlorChina"/>
| synonyms =
* ''Hesperopeuce'' <small>(Engelmann) Lemmon</small>
* ×''Hesperotsuga'' <small>C.N.Page</small>
* ''Micropeuce'' <small>(Spach) Gordon</small>
* ×''Tsugo-picea'' <small>Van Campo & Gaussen</small>
* ×''Tsugo-piceo-picea'' <small>Van Campo & Gaussen</small>
* ×''Tsugo-piceo-tsuga'' <small>Van Campo & Gaussen</small>
}}
[[File:Tsuga heterophylla1.jpg|thumb|''[[Tsuga heterophylla]]'']]
'''''Tsuga''''' ({{IPAc-en|ˈ|s|uː|ɡ|ə}},<ref>''Sunset Western Garden Book,'' 1995:606–607</ref> from [[Japanese language|Japanese]] {{lang|ja|栂}} ({{lang|ja|ツガ}}), the name of ''[[Tsuga sieboldii]]'') is a [[genus]] of [[conifer]]s in the subfamily [[Abietoideae]] of [[Pinaceae]], the pine family. The [[English-language]] [[common name]] "'''hemlock'''" arose from a perceived similarity in the smell of its crushed foliage to that of the unrelated plant [[Conium maculatum|hemlock]].<ref name=Mitchell>{{cite web |last=Mitchell|first=Alan| title=Conifers in the British Isles: a descriptive handbook |date=1972 | url=https://cdn.forestresearch.gov.uk/1972/03/fcbk033.pdf |page=302 |access-date=2024-10-24}}</ref> Unlike the latter, ''Tsuga'' species are not poisonous.<ref name="Farjon2010">{{cite book |last= Farjon |first= A. |date= 2010 |title= A handbook of the world's Conifers |volume= 2 |pages= 533–1111 |publisher= [[Brill Publishers]] |isbn= 978-90-04-17718-5 | quote = Tsuga is the Japanese name for Hemlock (the conifer, not the poisonous herb ''Conium maculatum'' in  ''Apiaceae''). | url = https://books.google.com/books?id=nqkKTQcGOtYC}}</ref>

The genus comprises eight to ten species (depending on the [[Taxonomic authority|authority]]), with four species occurring in [[North America]] and four to six in eastern [[Asia]].<ref name="Farjon1990">{{cite book |last= Farjon |first= A. |date= 1990 |title= Pinaceae. Drawings and Descriptions of the Genera |publisher= Koeltz Scientific Books |isbn= 3-87429-298-3 }}</ref><ref name="Rushforth">{{cite book |last= Rushforth |first= K. |date= 1987 |title= Conifers |publisher= Helm |isbn= 0-7470-2801-X }}</ref><ref name="GymDat">{{Gymnosperm Database |family= Pinaceae |genus= Tsuga |access-date= 2007-05-16 |ref= {{harvid|Gymnosperm Database}} }}</ref><ref name="FlorChina">{{eFloras|2|133931|Tsuga |family= Pinaceae |first1= Liguo |last1= Fu |first2= Nan |last2= Li |first3= Thomas S. |last3= Elias |first4= Robert R. |last4= Mill |access-date= 2007-05-16 |ref= {{harvid|Flora of China}} }}</ref><ref name="FloNA">{{eFloras|1|133931|Tsuga |family= Pinaceae |first= Ronald J. |last= Taylor |access-date= 2007-05-16 |ref= {{harvid|Flora of North America}}
}}</ref>

==Description==
They are medium-sized to large [[evergreen]] [[tree]]s, ranging from {{convert|10|-|60|m|abbr=off}} tall, with a conical to irregular crown, the latter occurring especially in some of the Asian species. The leading shoots generally droop. The [[Bark (botany)|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 (botany)|shoot]]s, which are present in many [[gymnosperm]]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 with [[pulvini]] that persist after the [[leaves]] fall. The winter [[bud]]s are ovoid or globose, usually rounded at the apex and not resinous.

The leaves are flattened to slightly angular and range from {{convert|5|-|35|mm|abbr=off|frac=16}} long and {{convert|1|-|3|mm|abbr=on|frac=32}} 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 (botany)|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]]tal bands (which are inconspicuous on ''[[Tsuga mertensiana|T.&nbsp;mertensiana]]'') separated by an elevated midvein. The upper surface of the leaves lack stomata, except those of ''T.&nbsp;mertensiana''. They have one resin canal that is present beneath the single vascular bundle.<ref name="Farjon1990"/><ref name="Rushforth"/><ref name="GymDat"/><ref name="FlorChina"/><ref name="FloNA"/>

The [[pollen]] cones grow solitary from lateral buds. They are {{convert|3|-|5|mm|abbr=on|frac=32}}{{Snd}}usually up to {{convert|5|mm|abbr=on|disp=or|frac=16}}{{Snd}}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]] are borne on year-old twigs and are small ovoid-globose or oblong-cylindric, ranging from {{convert|15|-|40|mm|abbr=on|frac=8}} long, except in ''T.&nbsp;mertensiana'', where they are cylindrical and longer, {{convert|35|-|80|mm|abbr=on|frac=4}} in length; they are solitary, terminal or rarely lateral, pendulous, and are [[Sessility (botany)|sessile]] or on a short peduncle up to {{convert|4|mm|abbr=on|frac=16}} long. Maturation occurs in 5–8 months, and the [[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]]s are included and small. The seeds are small, from {{convert|2|to|4|mm|abbr=on|frac=32}} long, and winged, with the wing being {{convert|8|to|12|mm|abbr=on|frac=16}} in length. They also contain small adaxial resin [[Vesicle (biology)|vesicles]]. Seed germination is [[epigeal germination|epigeal]]; the seedlings have 4–6 [[cotyledon]]s.<ref name="Farjon1990"/><ref name="Rushforth"/><ref name="GymDat"/><ref name="FlorChina"/><ref name="FloNA"/>

==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 colour; and the cones are the longest in the genus, {{convert|35|-|80|mm|abbr=on|frac=16}} long and cylindrical rather than ovoid. Some botanists treat it in a distinct genus as ''Hesperopeuce mertensiana'' (Bong.) Rydb.,<ref name="Page1990">{{cite encyclopedia |last=Page |first=C. N. |date=1990 |contribution=Pinaceae |pages=319–331 |editor-last=Kubitzki |editor-first=K. |title=The Families and Genera of Vascular Plants |publisher=Springer-Verlag |place=Berlin }}</ref> though it is more generally only considered distinct at the rank of subgenus.<ref name="Farjon1990"/>

The oldest fossils attributed to the genus are twigs, known from the Early Cretaceous of Inner Mongolia, China, though their relationship to modern ''Tsuga'' is not unambiguous. The earliest pollen attributed to the genus is known from the Upper Cretaceous of Poland, dating to around 90 million years ago. Abundant remains are only known from [[Eocene]] onwards, when the modern ''Tsuga'' [[crown group]] is thought to have begun to diversify.<ref name="WuZhou2020" /><ref>{{Cite journal |last1=Li |first1=Ya |last2=Gee |first2=Carole T. |last3=Tan |first3=Zhen-Zhen |last4=Zhu |first4=Yan-Bin |last5=Yi |first5=Tie-Mei |last6=Li |first6=Cheng-Sen |date=January 2024 |title=Exceptionally well-preserved seed cones of a new fossil species of hemlock, Tsuga weichangensis sp. nov. (Pinaceae), from the Lower Miocene of Hebei Province, North China |url=https://onlinelibrary.wiley.com/doi/10.1111/jse.12952 |journal=Journal of Systematics and Evolution |language=en |volume=62 |issue=1 |pages=164–180 |doi=10.1111/jse.12952 |bibcode=2024JSyEv..62..164L |issn=1674-4918|url-access=subscription }}</ref> While formerly present in the region ''Tsuga'' became extinct in Europe during the [[Middle Pleistocene]] epoch around 780-440,000 years ago, due to unfavourable climate change caused by the ongoing [[Quaternary glaciation]].<ref>{{Cite journal |last1=Xiao |first1=Shumei |last2=Li |first2=Shufeng |last3=Huang |first3=Jian |last4=Wang |first4=Xiaojun |last5=Wu |first5=Mengxiao |last6=Karim |first6=Rizwan |last7=Deng |first7=Weiyudong |last8=Su |first8=Tao |date=January 2024 |title=Influence of climate factors on the global dynamic distribution of Tsuga (Pinaceae) |journal=Ecological Indicators |language=en |volume=158 |pages=111533 |doi=10.1016/j.ecolind.2023.111533|doi-access=free |bibcode=2024EcInd.15811533X }}</ref>

[[File:2013-08-25 15 39 09 Closeup of Eastern Hemlock foliage across Taborton Road from the entrance to Spring Lake in Berlin, New York.jpg|thumb|''[[Tsuga canadensis|T. canadensis]]'' leaves are retained for 3–4 (–5) years]]
[[File:Tsuga-diversifolia.JPG|thumb|''[[Tsuga diversifolia|T. diversifolia]]'' foliage and cones in snow]]
[[File:MountainHemlock 6739.jpg|thumb|''[[Tsuga mertensiana|T. mertensiana]]'' foliage and cones]]

Another species, bristlecone hemlock, first described as ''T.&nbsp;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]]''.<ref name="Farjon1990"/><ref name="GymDat"/>

===Phylogeny===
{| class="wikitable"
|-
! colspan=1 |Phylogeny of ''Tsuga''<ref>{{cite journal |last1=Stull |first1=Gregory W. |last2=Qu |first2=Xiao-Jian |last3=Parins-Fukuchi |first3=Caroline |last4=Yang |first4=Ying-Ying |last5=Yang |first5=Jun-Bo |last6=Yang |first6=Zhi-Yun |last7=Hu |first7=Yi  |last8=Ma |first8=Hong |last9=Soltis |first9=Pamela S. |last10=Soltis |first10=Douglas E. |last11=Li |first11=De-Zhu |last12=Smith |first12=Stephen A. |last13=Yi |first13=Ting-Shuang |display-authors=et al. |year=2021 |title=Gene duplications and phylogenomic conflict underlie major pulses of phenotypic evolution in gymnosperms |journal=Nature Plants |url=https://www.biorxiv.org/content/biorxiv/early/2021/05/17/2021.03.13.435279.full.pdf |volume=7 |issue= 8|pages=1015–1025 |doi=10.1038/s41477-021-00964-4|biorxiv=10.1101/2021.03.13.435279 |pmid= 34282286|pmc= |bibcode= 2021NatPl...7.1015S|s2cid=232282918 |doi-access=}}</ref><ref>{{cite journal |last1=Stull |first1=Gregory W. |display-authors=et al. |year=2021 |title=main.dated.supermatrix.tree.T9.tre |publisher=Figshare |doi=10.6084/m9.figshare.14547354.v1 |url=https://figshare.com/articles/dataset/Gene_duplications_and_genomic_conflict_underlie_major_pulses_of_phenotypic_evolution_in_gymnosperms/14547354 |doi-access=}}</ref>
|- 
| style="vertical-align:top|
{{clade| style=font-size:90%;line-height:80%;
|label1=''Tsuga''
|1={{clade
  |label1=series
  |sublabel1=''Sieboldiae''
  |1={{clade
    |1=''[[Tsuga caroliniana|T. caroliniana]]'' <small>Engelmann</small>
    |2={{clade
      |1=''[[Tsuga diversifolia|T. diversifolia]]'' <small>(Maxim.) Masters</small>
      |2={{clade
        |1=''[[Tsuga sieboldii|T. sieboldii]]'' <small>Carrière</small>
        |2=''[[Tsuga chinensis|T. chinensis]]'' <small>(Franchet) Pritzel ex Diels</small>
         }}
       }}
     }}
  |label2=series
  |sublabel2=''Canadenses''
  |2={{clade
    |1={{clade
      |1=''[[Tsuga forrestii|T. forrestii]]'' <small>Downie</small>
      |2=''[[Tsuga dumosa|T. dumosa]]'' <small>(Don) Eichler</small>
       }}
    |2={{clade
      |1=''[[Tsuga canadensis|T. canadensis]]'' <small>(von Linné) Carrière</small>
      |2={{clade
        |1=''[[Tsuga heterophylla|T. heterophylla]]'' <small>(Rafinesque) Sargent</small>
        |2=''[[Tsuga mertensiana|T. mertensiana]]'' <small>(Bongard) Carrière</small>
         }}
       }}
     }}
   }}
}}
|}
The above phylogeny is in marked conflict with earlier studies, which found ''T. mertensiana'' as basal to the rest of the genus.<ref name="Farjon1990"/>

=== Species ===
; Accepted living species<ref name="WCSP">{{WCSP|379374|Tsuga}}</ref><ref>{{BONAP|genus=Tsuga|date=2013}}</ref><ref name="FlorChina" />
* ''[[Tsuga canadensis]]'' – eastern hemlock – Eastern Canada, Eastern United States
* ''[[Tsuga caroliniana]]'' – Carolina hemlock – Southern [[Appalachians]]
* ''[[Tsuga chinensis]]'' – Taiwan hemlock – [[Taiwan]], [[Tibet]], much of China
* ''[[Tsuga diversifolia]]'' – northern Japanese hemlock – [[Honshu]], [[Kyushu]]
* ''[[Tsuga dumosa]]'' – Himalayan hemlock – [[Himalayas]], Tibet, [[Yunnan]], [[Sichuan]]
* ''[[Tsuga forrestii]]'' – Forrest's hemlock – Sichuan, Yunnan, [[Guizhou]]
* ''[[Tsuga heterophylla]]'' – western hemlock – Western Canada, Northwestern United States
* ''[[Tsuga × jeffreyi]]''  – [[British Columbia]], [[Washington (state)|Washington]] (doubtful; often treated as a variety of ''T. mertensiana'', with no verified evidence of hybrid origin<ref name="Farjon1990"/><ref name="GymDat2">{{cite web | title=Tsuga mertensiana (mountain hemlock) description | website=The Gymnosperm Database | date=2024-07-21 | url=https://www.conifers.org/pi/Tsuga_mertensiana.php | access-date=2024-10-26}}</ref>)
* ''[[Tsuga mertensiana]]'' – mountain hemlock – [[Alaska]], British Columbia, Western United States
* ''[[Tsuga sieboldii]]'' – southern Japanese hemlock – Japan
* ''[[Tsuga ulleungensis]]'' – Ulleungdo hemlock – [[Ulleung Island]], Korea<ref name="NatGeo">{{cite web |last=Popkin |first=Gabe |date=30 January 2018 |title=First New Species of Temperate Conifer Tree Discovered in More Than a Decade |url=https://news.nationalgeographic.com/2018/01/ulleungdo-hemlock-tree-discovered-korea-wooly-adelgid/ |archive-url=https://web.archive.org/web/20180131024220/https://news.nationalgeographic.com/2018/01/ulleungdo-hemlock-tree-discovered-korea-wooly-adelgid/ |url-status=dead |archive-date=January 31, 2018 |access-date=31 January 2018 |publisher=National Geographic News}}</ref>

;Accepted paleospecies
* †''[[Tsuga aburaensis]]'' {{small|Tanai}} - Abura, [[Hokkaido]] ([[Miocene]])<ref name="Tanai1961">{{cite journal |last1=Tanai |first1=T. |year=1961 |title=Neogene floral change in Japan |url=https://eprints.lib.hokudai.ac.jp/dspace/bitstream/2115/35928/1/11(2)_119-398.pdf |journal=Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and Mineralogy |volume=11 |issue=2 |page=258}}</ref>
* †''[[Tsuga asiatica]]'' - [[Lawula Formation]], [[Tibet]] ([[Priabonian]])<ref name="WuZhou2020">{{Cite journal |last1=Wu |first1=M.-X. |last2=Huang |first2=J. |last3=Su |first3=T. |last4=Leng |first4=Q. |last5=Zhou |first5=Z.-K. |year=2020 |title=''Tsuga'' seed cones from the late Paleogene of southwestern China and their biogeographical and paleoenvironmental implications |journal=Palaeoworld |volume=29 |issue=3 |pages=617–628 |doi=10.1016/j.palwor.2019.07.005 |s2cid=199885815}}</ref>
* †''[[Tsuga europaea]]'' - Maria Mine, [[Alsdorf]], North Rhine-Westphalia (Miocene)<ref name="Europae">{{cite journal |last1=Menzel |first1=P. |year=1914 |title=Beitrag zur Flora der Niederrheinischen Braunkohlenformation |journal=Jahrbuch der Königlich Preussischen Geologischen Landesanstalt zu Berlin für das Jahr 1913 |language=German |volume=34 |pages=1–98}}</ref>
* †''[[Tsuga nanfengensis]]'' - [[Yunnan]] (Late Miocene)<ref name="Wang2015">{{cite journal |last1=Wang |first1=H.B. |last2=Bondarenko |first2=O.V. |last3=Jacques |first3=F.M.B. |last4=Wang |first4=Y.H. |last5=Zhou |first5=Z.K. |year=2015 |title=A New Species of ''Tsuga'' (Pinaceae) based on Lignified Wood from the Late Miocene of Central Yunnan, China, and Its Paleoenvironmental Implications |journal=Acta Geologica Sinica - English Edition |volume=89 |issue=5 |pages=1429–1439 |doi=10.1111/1755-6724.12555 |bibcode=2015AcGlS..89.1429W |s2cid=130310084}}</ref>
* †''[[Tsuga swedaea]]'' - [[Buchanan Lake Formation]], [[Axel Heiberg Island]] ([[Lutetian]])<ref name="LePage2003">{{cite journal |last1=Lepage |first1=B. A. |year=2003 |title=A new species of ''Tsuga'' (Pinaceae) from the middle Eocene of Axel Heiberg Island, Canada, and an assessment of the evolution and biogeographical history of the genus |journal=Botanical Journal of the Linnean Society |volume=141 |issue=3 |pages=257–296 |doi=10.1046/j.1095-8339.2003.00131.x |doi-access=}}</ref>
* †''[[Tsuga taxoides]]'' - [[Inner Mongolia]] ([[Early Cretaceous]])<ref name="Tan1982">{{cite book |last1=Tan |first1=L. |title=Mesozoic Strata Paleontology of Coal-bearing Basin in Guyang, Inner Mongolia |last2=Zhu |first2=J.N. |publisher=Geological Press, Beijing |year=1982 |location=Beijing |pages=149 |language=Chinese}}</ref>
* †''[[Tsuga weichangensis]]'' - [[Hebei]] (Miocene)
* †''[[Tsuga xianfengensis]]'' - Yunnan (Late Miocene)<ref name="WuZhou2020" />

; Formerly included<ref name="WCSP" />
Moved to other genera:
{{columns-list|colwidth=30em|
* ''T. ajanensis – [[Picea jezoensis]]''
* ''T. argyrophylla – [[Cathaya argyrophylla]]'' 
* ''T. balfouriana – [[Picea likiangensis]] var. rubescens'' 
* ''T. japonica – [[Pseudotsuga japonica]]'' 
* ''T. lindleyana – [[Pseudotsuga menziesii]] var. glauca''
* ''T. longibracteata – [[Nothotsuga longibracteata]]'' 
* ''T. macrocarpa – [[Pseudotsuga macrocarpa]]'' 
* ''T. mairei – [[Taxus mairei]]''
* ''T. roulletii – [[Keteleeria evelyniana]]''
}}

==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]]fall and tolerate [[ice storm]]s better than most other trees.<ref name="Farjon1990"/><ref name="GymDat"/>  Hemlock trees are more tolerant of heavy shade than other conifers; they are, however, more susceptible to drought.<ref name=HWAbiocontrol>{{cite web|title=Implementation and Status of Biological Control of the Hemlock Woody Adelgid|url=http://na.fs.fed.us/pubs/fhp/hemlocks/bio_control-2012.pdf|publisher=US Forest Service|access-date=28 July 2013|date=December 2011}}</ref>

=== Threats ===
The two eastern North American species, ''[[Tsuga canadensis|T.&nbsp;canadensis]]'' and ''[[Tsuga caroliniana|T.&nbsp;caroliniana]]'', are under serious threat by the sap-sucking [[insect]] ''Adelges tsugae'' ([[hemlock woolly adelgid]]).<ref>United States Forest Service: [http://www.na.fs.fed.us/fhp/hwa/ Hemlock Woolly Adelgid website]</ref> This adelgid, related to the [[aphid]]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 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]].<ref>USDA Forest Service NA-PR-05-92</ref> 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 [[finch]]es and small [[rodent]]s.

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.<ref name=pb>Phillips, D. H., & Burdekin, D. A. (1992). ''Diseases of Forest and Ornamental Trees''. Macmillan {{ISBN|0-333-49493-8}}.</ref>

==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 [[cultivar]]s have been selected for use in gardens. [[Tanbark|The&nbsp;bark]] is also used in [[Tanning (leather)|tanning]] leather.<ref name=handbook>{{ cite book | last1=Dallimore | first1=William | author1-link=William Dallimore | last2=Jackson | first2=Albert Bruce | author2-link=Albert Bruce Jackson | year=1966 | title=A handbook of Coniferae, including Ginkgoaceae | edition=4 | location=London | publisher=Edward Arnold | pages=632–648 }}</ref> The needles are sometimes used to make a tea and perfume.{{citation needed|date=October 2024}}

==References==
{{Reflist}}

==External links==
* {{Cite NIE|wstitle=Hemlock-tree|year=1905 |short=x}}
* {{Commons category-inline|Tsuga}}

{{Tannin source}}
{{Plant classification}}
{{Acrogymnospermae classification}}
{{Taxonbar|from=Q739430}}
{{Authority control}}

[[Category:Tsuga| ]]
[[Category:Conifer genera]]
[[Category:Taxa described in 1855]]
[[Category:Taxa named by Stephan Endlicher]]