Tsuga
| Tsuga | |
|---|---|
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| Tsuga heterophylla | |
Scientific classification 
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| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Pinophyta |
| Class: | Pinopsida |
| Order: | Pinales |
| Family: | Pinaceae |
| Subfamily: | Abietoideae |
| Genus: | Tsuga (Endlicher) Carrière
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| Synonyms[1][2] | |
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Tsuga (
The genus comprises eight to ten species (depending on the
Description
They are medium-sized to large
The leaves are flattened to slightly angular and range from 5–35 millimetres (3⁄16–1+3⁄8 inches) long and 1–3 mm (1⁄32–1⁄8 in) 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 (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.[5][6][7][2][8]
The
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 (1+3⁄8–3+1⁄8 in) 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]
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.[5][7]
Phylogeny
| Phylogeny of Tsuga[10][11] | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Species
- Tsuga canadensis – eastern hemlock – Eastern Canada, Eastern United States
- 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
- Tsuga mertensiana – mountain hemlock – Alaska, British Columbia, Western United States
- Tsuga sieboldii – southern Japanese hemlock – Japan
- Ulleung Island, Korea[13]
- Accepted paleospecies
- †Tsuga aburaensis Tanai - Abura, Hokkaido (Miocene)[14]
- †Tsuga asiatica - Lawula Formation, Tibet (Priabonian)[15]
- †Tsuga europaea - Maria Mine, Alsdorf, North Rhine-Westphalia (Miocene)[16]
- †Tsuga nanfengensis - Yunnan (Late Miocene)[17]
- †Tsuga swedaea - Buchanan Lake Formation, Axel Heiberg Island (Lutetian)[18]
- †Tsuga taxoides - Inner Mongolia (Early Cretaceous)[19]
- †Tsuga xianfengensis - Yunnan (Late Miocene)[15]
- Formerly included[1]
Moved to other genera:
- T. ajanensis – Picea jezoensis
- T. argyrophylla – Cathaya argyrophylla
- T. balfouriana – Picea likiangensis var. rubescens
- T. japonica – Pseudotsuga japonica
- T. lindleyana – Pseudotsuga menziesiivar. 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 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.[20]
Threats
The two eastern North American species, .
Old trees are commonly attacked by various
Uses
The wood obtained from hemlocks is important in the timber industry, especially for use as
References
- ^ a b c "Tsuga". World Checklist of Selected Plant Families (WCSP). Royal Botanic Gardens, Kew.
- ^ a b c d e Fu, Liguo; Li, Nan; Elias, Thomas S.; Mill, Robert R. "Tsuga". Flora of China. Vol. 4. Retrieved 2007-05-16 – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
- ^ Sunset Western Garden Book, 1995:606–607
- ^ Farjon, A. (2010). A handbook of the world's Conifers. Vol. 2. Brill Publishers. pp. 533–1111.
- ^ ISBN 3-87429-298-3.
- ^ ISBN 0-7470-2801-X.
- ^ a b c d e Earle, Christopher J., ed. (2018). "Tsuga". The Gymnosperm Database. Retrieved 2007-05-16.
- ^ a b c Taylor, Ronald J. (1993). "Tsuga". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). Vol. 2. New York and Oxford: Oxford University Press. Retrieved 2007-05-16 – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
- ^ Page, C. N. (1990). "Pinaceae". In Kubitzki, K. (ed.). The Families and Genera of Vascular Plants. Berlin: Springer-Verlag. pp. 319–331.
- S2CID 232282918.
- )
- ^ "Tsuga". County-level distribution maps from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2013.
- ^ Popkin, Gabe (30 January 2018). "First New Species of Temperate Conifer Tree Discovered in More Than a Decade". National Geographic News. Archived from the original on January 31, 2018. Retrieved 31 January 2018.
- ^ Tanai, T. (1961). "Neogene floral change in Japan" (PDF). Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and Mineralogy. 11 (2): 258.
- ^ S2CID 199885815.
- ^ Menzel, P. (1914). "Beitrag zur Flora der Niederrheinischen Braunkohlenformation". Jahrbuch der Küniglich Preussichen Geologischen Landesanstalt zur Berlin für das Jahr 1913 (in German). 34: 1–98.
- S2CID 130310084.
- .
- ^ Tan, L.; Zhu, J.N. (1982). Mesozoic Strata Paleontology of Coal-bearing Basin in Guyang, Inner Mongolia (in Chinese). Beijing: Geological Press, Beijing. p. 149.
- ^ "Implementation and Status of Biological Control of the Hemlock Woody Adelgid" (PDF). US Forest Service. December 2011. Retrieved 28 July 2013.
- ^ United States Forest Service: Hemlock Woolly Adelgid website
- ^ USDA Forest Service NA-PR-05-92
- ISBN 0-333-49493-8.
External links
- . New International Encyclopedia. 1905.
Media related to Tsuga at Wikimedia Commons
