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Ulmus pumila

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Ulmus pumila
Gobi Desert of Mongolia
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Rosales
Family: Ulmaceae
Genus: Ulmus
Species:
U. pumila
Binomial name
Ulmus pumila
Synonyms
  • Ulmus campestris var. pumila Ledeb.
  • Ulmus campestris L. var. pumila (L.) Maxim.
  • Ulmus gobicus Anon.
  • Ulmus humilis Amman ex Steud.
  • Ulmus manshurica Nakai
  • Ulmus microphylla Persoon
  • Ulmus pumila var. genuina Skvort.
  • Ulmus pumila var. microphylla Persoon
  • Ulmus pumila var. transbaicalensis Pallas

Ulmus pumila, the Siberian elm, is a tree native to Asia. It is also known as the Asiatic elm and dwarf elm, but sometimes miscalled the 'Chinese elm' (Ulmus parvifolia). U. pumila has been widely cultivated throughout Asia, North America, Argentina, and southern Europe, becoming naturalized in many places, notably across much of the United States.[2][3]

Description

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The Siberian elm is usually a small to medium-sized, often bushy, deciduous tree growing to 25 metres (82 feet) tall, the diameter at breast height to 1 m (3 ft 3 in). The bark is dark gray, irregularly longitudinally fissured. The branchlets are yellowish gray, glabrous or pubescent, unwinged and without a corky layer, with scattered lenticels. The winter buds dark brown to red-brown, globose to ovoid. The petiole is 4–10 millimetres (1⁄4–1⁄2 inch), pubescent, the leaf blade elliptic-ovate to elliptic-lanceolate, 2–8 by 1.2–3.5 centimetres (3⁄4 in–3+1⁄8 in × 1⁄2 in–1+3⁄8 in),[4] the colour changing from dark green to yellow in autumn.[5] The perfect, apetalous wind-pollinated flowers bloom for one week in early spring, before the leaves emerge, in tight fascicles (bundles) on the last year's branchlets.[6][7] Flowers emerging in early February are often damaged by frost (causing the species to be dropped from the Dutch elm breeding programme).[8] Each flower is about 3 mm (1⁄8 in) across and has a green calyx with 4–5 lobes, 4–8 stamens with brownish-red anthers,[9] and a green pistil with a two-lobed style.[7][10] Unlike most elms, the Siberian elm is able to self-pollinate successfully.[11]

The wind-dispersed samarae are whitish tan, orbicular to rarely broadly obovate or elliptical, 1 cm–2 cm × 1 cm–1.5 cm (3⁄8 in–3⁄4 in × 3⁄8 in–5⁄8 in), glabrous except for pubescence on stigmatic surface; the stalk 1–2 mm (5⁄128–5⁄64 in), the perianth persistent. The seed is at centre of the samara or occasionally slightly toward apex but not reaching the apical notch. Flowering and fruiting occur March to May. Ploidy: 2n = 28.[5] The tree also suckers readily from its roots.[12]

The tree is short-lived in temperate climates, rarely reaching more than 60 years of age, but in its native environment may live to between 100 and 150 years.[13][14] A giant specimen, 45 kilometres (28 miles) southeast of Khanbogt in the south Gobi, with a girth of 5.55 m (18 ft 3 in) in 2009, may exceed 250 years (based on average annual ring widths of other U. pumila in the area).[citation needed]

  • Bark of mature tree, Korea
    Bark (Korea)
  • Stump showing rapid stem diameter increase (>40 millimetres (1+1⁄2 in) per annum)
    Stump showing rapid stem diameter increase (>40 millimetres (1+1⁄2 in) per annum)
  • Summer foliage
    Summer foliage
  • Typical 'long shoots' of pendulous forms
    Typical 'long shoots' of pendulous forms
  • Axil buds and fawn-coloured twigs
    Axil buds and fawn-coloured twigs
  • Flowers
    Flowers
  • Immature fruits (and Satyrium w-album larva)
    Immature fruits (and Satyrium w-album larva)
  • Mature fruits
    Mature fruits

Taxonomy

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The species was described by Peter Simon Pallas in the 18th century from specimens from Transbaikal.

Two varieties were traditionally recognized: var. pumila and var. arborea, the latter now treated as a cultivar, U. pumila 'Pinnato-ramosa'.

Distribution and habitat

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The tree is native to Central Asia, eastern Siberia, the Russian Far East, Mongolia, Tibet, northern China, India (northern Kashmir) and Korea.[5][6][15] It is the last tree species encountered in the semi-desert regions of Central Asia.[16]

Ecology

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Tree sparrow with seed, Ukraine
U. pumila spreading along the banks of the Columbia River, Washington state, 2013

Pests and diseases

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The tree has considerable variability in resistance to Dutch elm disease; for example, trees from north-western and north-eastern China exhibit significantly higher tolerance than those from central and southern China.[17][18] Moreover, it is highly susceptible to damage from many insects and parasites, including the elm leaf beetle Xanthogaleruca luteola,[19] the Asian 'zigzag' sawfly Aproceros leucopoda,[20] Elm Yellows,[21] powdery mildew, cankers,[22] aphids, leaf spot and, in the Netherlands, coral spot fungus Nectria cinnabarina.[23] U. pumila is the most resistant of all the elms to verticillium wilt.[24]

Invasiveness and spontaneous hybridization

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In North America, Ulmus pumila has become an invasive species in much of the region from central Mexico[25] northward across the eastern and central United States to Ontario, Canada.[26] It also hybridizes in the wild with the native U. rubra (slippery elm) in the central United States, prompting conservation concerns for the latter species.[27][28] In South America, the tree has spread across much of the Argentine pampas.[29][30]

In Europe it has spread widely in Spain, and hybridizes extensively there with the native field elm (U. minor),[31] contributing to conservation concerns for the latter species.[32] Research is ongoing into the extent of hybridisation with U. minor in Italy.[33]

Ulmus pumila is often found in abundance along railroads and in abandoned lots and on disturbed ground. The gravel along railroad beds provides ideal conditions for its growth: well-drained, nutrient poor soil, and high light conditions; these beds provide corridors which facilitate its spread. It is found as high as 8000 feet in the Sandia Mountains in New Mexico and is invading coniferous forest there. New Mexico may be a center of genetic diversity in North America. Owing to its high sunlight requirements, it seldom invades mature forests, and is primarily a problem in cities and open areas,[34][35] as well as along transportation corridors.

The species is now listed in Japan as an alien species recognized as established in Japan or found in the Japanese wild.[36]

Cultivation

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U. pumila was introduced into Spain as an ornamental, probably during the reign of Philip II (1556–98),[37] and from the 1930s into Italy.[33] In these countries it has naturally hybridized with the field elm (U. minor). In Italy it was widely used in viniculture, notably in the Po valley, to support the grape vines until the 1950s, when the demands of mechanization made it unsuitable.

Three specimens were supplied by the Späth nursery of Berlin to the Royal Botanic Garden Edinburgh (RBGE) in 1902 as U. pumila,[38] in addition to specimens of the narrow-leaved U. pumila cultivar 'Pinnato-ramosa'.[39] One was planted in RBGE; the two not planted in the Garden may survive in Edinburgh, as it was the practice of the Garden to distribute trees about the city.[39] Kew Gardens obtained specimens of U. pumila from the Arnold Arboretum in 1908 and, as U. pekinensis, via the Veitch Nurseries in 1910 from William Purdom in northern China.[40] A specimen obtained from Späth and planted in 1914 stood in the Ryston Hall arboretum, Norfolk,[41] in the early 20th century.[42] The tree was propagated and marketed by the Hillier & Sons nursery, Winchester, Hampshire, from 1962 to 1977, during which time over 500 were sold.[43][44] More recently, the popularity of U. pumila in the Great Britain has been almost exclusively as a bonsai subject, and mature trees are largely restricted to arboreta.[citation needed] In the UK the TROBI Champions grow at Thorp Perrow Arboretum, Yorkshire, 19 m (62 ft 4 in) × 70 cm (2 ft 4 in) in 2004, and at St Ann's Well Gardens, Hove, Sussex 20 m (65 ft 7 in) × 60 cm (2 ft 0 in) in 2009.[45]

U. pumila is said to have been introduced to the US in 1905 by Prof. John George Jack,[22] and later by Frank Nicholas Meyer, though 'Siberian elm' appears in some 19th-century US nursery catalogues.[46] The tree was cultivated at the United States Department of Agriculture (USDA) Experimental Station at Mandan, North Dakota, where it flourished.[47] It was consequently selected by the USDA for planting in shelter belts across the prairies in the aftermath of the Dustbowl disasters, where its rapid growth and tolerance for drought and cold initially made it a great success. However, the species later proved susceptible to numerous maladies. Attempts to find a more suitable cultivar were initiated in 1997 by the Plant Materials Center of the USDA, which established experimental plantations at Akron, Colorado, and Sidney, Nebraska. The study, no. 201041K, will conclude in 2020.[citation needed] The US National Champion, measuring 33.5 m (109 ft 11 in) high in 2011, grows in Berrien County, Michigan.[48][49]

The seeds lose their viability rapidly after maturity unless placed on suitable germination conditions or dried and placed at low temperatures.[50] The species has a high sunlight requirement and is not shade-tolerant; with adequate light it exhibits rapid growth. The tree is also fairly intolerant of wet ground conditions, growing better on well-drained soils. While it is very resistant to drought and severe cold, and able to grow on poor soils, its short period of dormancy, flowering early in spring followed by continuous growth until the first frosts of autumn,[51] renders it vulnerable to frost damage.

As an ornamental U. pumila is a very poor tree, tending to be short-lived, with brittle wood and poor crown shape, but it has nevertheless enjoyed some popularity owing to its rapid growth and provision of shade. The Siberian Elm has been described as "one of the world's worst... ornamental trees that does not deserve to be planted anywhere".[52] Yet in the US during the 1950s, the tree was also widely promoted as a fast-growing hedging substitute for privet, and as a consequence is now commonly found in nearly all states.[47]

Cultivars

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Valued for the high resistance of some clones to Dutch elm disease, over a dozen selections have been made to produce hardy ornamental cultivars, although several may no longer be in cultivation:


A variegated weeping elm, with cream, dark green and light green variegation, is cultivated in China as Ulmus pumila 'Variegata'.[53][54][55][56]

Some authorities consider the cultivar 'Berardii' a form of U. pumila.[57][58] Nottingham elm, considered an Ulmus × hollandica by Richens, was marketed from the 19th century as 'Siberian elm'.

Hybrid cultivars

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The species has been widely hybridized in the United States and Italy to create robust trees of more native appearance with high levels of resistance to Dutch elm disease:

Other hybrid cultivars involving crossings with U. pumila:

Uses

[edit]

The unripe seeds have long been eaten by the peoples of Manchuria, and during the Great Chinese Famine they also became one of the most important foodstuffs in the Harbin region. The leaves were also gathered, to the detriment of the trees, prompting a prohibition order by the authorities, which was largely ignored. The leaves eaten raw are not very palatable, but stewed and prepared with Kaoliang or Foxtail millet make a better tasting and more filling meal.[59]

Ulmus pumila in literature and travel writing

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U. pumila open woodland in the sandy steppe in Bayannuur sum, Bulgan Province, Mongolia, 2008

The "dwarf-"[60] or "shrub-elms"[61] of the North Caucasus, along with other local flora, appear in the opening description of Tolstoy's story 'The Raid' (1853).

Nicholas Roerich describes a specimen discovered on his travels through Mongolia:[62]

We are in the deserts of Mongolia. It was hot and dusty yesterday. From faraway thunder was approaching. Some of our friends became tired from climbing the stony holy hills of Shiret Obo. While already returning to the camp, we noticed in the distance a huge elm tree – 'karagatch', - lonely, towering amidst the surrounding endless desert. The size of the tree, its somewhat familiar outlines attracted us into its shadow. Botanical considerations led us to believe that in the wide shade of the giant there might be some interesting herbs. Soon, all the co-workers gathered around the two mighty stems of the karagatch. The deep, deep shadow of the tree covered about 50 feet across. The powerful tree-stems were covered with fantastic burr growths. In the rich foliage, birds were singing and the beautiful branches were stretched out in all directions, as if wishing to give shelter to all pilgrims.

Accessions

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North America

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Europe

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Australasia

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Africa

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Nurseries

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Europe

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  • Van Den Berk (UK) Ltd., [6], London, UK

References

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  1. ^ Barstow, M. (2018). "Ulmus pumila". IUCN Red List of Threatened Species. 2018: e.T61967372A61967374. doi:10.2305/IUCN.UK.2018-1.RLTS.T61967372A61967374.en. Retrieved 6 June 2023.
  2. ^ "Ulmus pumila". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014.
  3. ^ Hirsch, H.; Brunet, J.; Zalapa, J.; Von Wehrden, H.; Hartmann, M.; Kleindienst, C.; Schlautman, B.; Kosman, E.; Wesche, K.; Renison, D.; Hensen, I. (2017). "Intra- and interspecific hybridization in invasive Siberian elm". Biol Invasions. 19 (6): 1889–1904. doi:10.1007/s10530-017-1404-6. hdl:10019.1/122672. S2CID 42755808.
  4. ^ "Herbarium specimen - E00824809". Herbarium Catalogue. Royal Botanic Garden Edinburgh. Leaves specimen from Harbin, Manchuria (1953); Muséum national d'Histoire naturelle, Paris; herbarium specimen P06883116, labelled Ulmus, Mongolia
  5. ^ a b c Fu, L., Xin, Y. & Whittemore, A. (2002). Ulmaceae, in Wu, Z. & Raven, P. (eds) Flora of China, Vol. 5 (Ulmaceae through Basellaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, US. [1]
  6. ^ a b Fu, Liguo; Xin, Yiqun; Whittemore, Alan. "Ulmus pumila". Flora of China. Vol. 5 – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  7. ^ a b Sherman-Broyles, Susan L. (1997). "Ulmus pumila". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). Vol. 3. New York and Oxford: Oxford University Press – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  8. ^ Went, J. (1954). The Dutch Elm Disease – Summary of fifteen years' hybridization and selection work (1937–1952). European Journal of Plant Pathology. 02(1954); 60(2): 109–1276.
  9. ^ Hilty, John (2020). "Siberian Elm (Ulmus pumila)". Illinois Wildflowers. Retrieved 6 June 2023.
  10. ^ Sherman-Broyles, Susan L. (1997). "Ulmus". In Flora of North America Editorial Committee (ed.). Flora of North America North of Mexico (FNA). Vol. 3. New York and Oxford: Oxford University Press – via eFloras.org, Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
  11. ^ Townsend, A. M. (1975). "Crossability patterns and morphological variation among elm species and hybrids". Silvae Genetica. 24 (1): 18–23. ISSN 0037-5349.
  12. ^ Grbić, M., Skočajić, D., Đukić, M., Đunisijević-Bojović, D., Marković, M. (2015). 'Mass clonal propagation of elm as a way for replacement of endangered autochthonous species'. p.62. Proceedings, International Conference Reforestation Challenges, 3–6 June 2015, Belgrade, Serbia.
  13. ^ "Untitled". Archived from the original on 2007-11-13. Retrieved 2008-01-04.
  14. ^ "Pictures".
  15. ^ "Ulmus pumila". Germplasm Resources Information Network. Agricultural Research Service, United States Department of Agriculture. Retrieved 8 September 2016.
  16. ^ Solla, A.; Martín, J. A.; Corral, P.; Gil, L. (2005). "Seasonal changes in wood formation of Ulmus pumila and U. minor and its relation with Dutch elm disease". New Phytologist. 166 (3): 1025–1034. doi:10.1111/j.1469-8137.2005.01384.x. PMID 15869660.
  17. ^ Smalley, E. & Guries, R. P. (1993). "Breeding elms for resistance to Dutch elm disease". Annual Review of Phytopathology. 31: 325–352. doi:10.1146/annurev.py.31.090193.001545.
  18. ^ Zalapa, Juan E.; Brunet, Johanne; Guries, Raymond P. (2008). "Genetic diversity and relationships among Dutch elm disease tolerant Ulmus pumila L. Accessions from China". Genome. 51 (7): 492–500. doi:10.1139/G08-034. PMID 18545273. S2CID 28606171.
  19. ^ Miller, F. & Ware, G. (2001). "Resistance of Temperate Chinese Elms (Ulmus spp.) to Feeding of the Adult Elm Leaf Beetle (Coleoptera: Chrysomelidae)". Journal of Economic Entomology. 94 (1): 162–166. doi:10.1603/0022-0493-94.1.162. PMID 11233108. S2CID 42980569.
  20. ^ Blank, S.; Kohler, T.; Pfannenstill, T.; Liston, A. (2013). "Zig-zagging across Central Europe: recent range extension, dispersal speed and larval hosts of Aproceros leucopoda (Hymenoptera, Argidae) in Germany". Journal of Hymenoptera Research. 41: 57–74. doi:10.3897/JHR.41.8681.
  21. ^ Mittempergher, L; Santini, A (2004). "The history of elm breeding". Forest Systems. 13 (1): 161–177. Retrieved 6 June 2023.
  22. ^ a b Leopold, D. J. (1980). "Chinese and Siberian elms". Journal of Arboriculture. 6 (7): 175–179. Retrieved 6 June 2023 – via Arboriculture & Urban Forestry Online.
  23. ^ Heybroek, Hans M. (1957). "Elm breeding in the Netherlands". Silvae Genetica. 6 (3–4): 112–117. Retrieved 6 June 2023 – via Wageningen University & Research.
  24. ^ Pegg, G. F. & Brady, B. L. (2002). Verticillium Wilts. CABI Publishing. ISBN 978-0-85199-529-8.
  25. ^ Todzia, C. A. & Panero, J. L. (1998). "A new species of Ulmus (Ulmaceae) from southern Mexico and a synopsis of the species in Mexico". Brittonia. 50 (3): 343–347. doi:10.2307/2807778. JSTOR 2807778. S2CID 21320752.
  26. ^ McIlvain, E. H. & Armstrong, C. G. (1965). Siberian Elm: A Tough New Invader of Grasslands. Weeds, Vol. 13, No. 3 (July 1965), pp 278 – 279. Weed Science Society of America & Allen Press.
  27. ^ J. E. Zalapa; J. Brunet; R. P. Guries (June 28, 2008). "Isolation and characterization of microsatellite markers for red elm (Ulmus rubra Muhl.) and cross-species amplification with Siberian elm (Ulmus pumila L.)". Mol Ecol Resour. 8 (1): 109–12. doi:10.1111/j.1471-8286.2007.01805.x. PMID 21585729. S2CID 7294817.
  28. ^ Elowsky, C. G., Jordon-Thaden, I. E., & Kaul, R. B. (2013). A morphological analysis of a hybrid swarm of native Ulmus rubra and introduced U. pumila (Ulmaceae) in southern Nebraska. Phytoneuron 2013-44: 1–23. ISSN 2153-733X.
  29. ^ Villamil, C. B., Zalba, S. M. Red de información sobre especies exóticas invasoras – I3N-Argentina Universidad Nacional del Sur Bahía Blanca, Argentina.
  30. ^ Hiersch, H., Hensen, I., Zalapa, J. Guries, R. & Brunet, J. (2013). Is hybridization a necessary condition for the evolution of invasiveness in non-native Siberian elm? Abstracts. Third International Elm Conference 2013. The elm after 100 years of Dutch elm disease. Florence, p45.
  31. ^ U. carpinifolia × U. pumila, Morton Arboretum, Illinois, cirrusimage.com
  32. ^ Cogolludo-Agustín, Miguel ángel; Agúndez, Dolores; Gil, Luis (2000). "Identification of native and hybrid elms in Spain using isozyme gene markers". Heredity. 85 (2): 157–166. doi:10.1046/j.1365-2540.2000.00740.x. PMID 11012718.
  33. ^ a b Brunet, Johanne; Zalapa, Juan E.; Pecori, Francesco; Santini, Alberto (14 May 2013). "Hybridization and introgression between the exotic Siberian elm, Ulmus pumila, and the native Field elm, U. minor, in Italy". Biol Invasions. 15 (12): 2717–2730. doi:10.1007/s10530-013-0486-z. S2CID 14385250.
  34. ^ National Audubon Society (2002). Field Guide to North American Trees, Western Region, p. 419-420
  35. ^ "Ulmus pumila (PIER species info)". Pacific Island Ecosystems at Risk project (PIER)).
  36. ^ Mito, Toshikazu; Uesugi, Tetsuro (2004). "Invasive Alien Species in Japan: The Status Quo and the New Regulation for Prevention of their Adverse Effects" (PDF). Airies. Archived from the original (PDF) on 2012-03-22. Retrieved 2011-03-30.
  37. ^ Cogolludo-Agustín, Miguel Ángel; Agúndez, Dolores; Gil, Luis (1 August 2000). "Identification of native and hybrid elms in Spain using isozyme gene markers". Heredity. 85 (2): 157–166. doi:10.1046/j.1365-2540.2000.00740.x. PMID 11012718.
  38. ^ "Herbarium specimen - E00824808". Herbarium Catalogue. Royal Botanic Garden Edinburgh. "Herbarium specimen - E00824813". Herbarium Catalogue. Royal Botanic Garden Edinburgh. U. pumila herbarium leaf-specimens, RBGE 1902: elmer.rbge.org
  39. ^ a b Accessions book. Royal Botanic Garden Edinburgh. 1902. pp. 45, 47.
  40. ^ Elwes and Henry (1913), p.1927
  41. ^ rystonhall.co.uk/
  42. ^ Ryston Hall Arboretum catalogue. c. 1920. pp. 13–14.
  43. ^ Hillier & Sons (1977). Catalogue of Trees & Shrubs. Hillier, Ampfield, UK.
  44. ^ Hillier & Sons Sales inventory 1962 to 1977 (unpublished).
  45. ^ Johnson, O. (ed.). (2011). Champion Trees of Britain & Ireland. Royal Botanic Gardens, Kew, London. ISBN 978-1-84246-452-6
  46. ^ Hovey & Co., Boston, Mass., Catalogue of ornamental trees & shrubs, evergreens and climbing plants, 1855, p.5
  47. ^ a b Klingaman, G. (1999). Plant of the Week: Siberian Elm. Extension News, University of Arkansas, Division of Agriculture.
  48. ^ American Forests. (2012). The 2012 National Register of Big Trees.
  49. ^ americanforests.org
  50. ^ Hirsch, H., Wypior, C., Wehrden, H., Wesche, K., Renison, D, and Hensen, I. (2012). Germination performance of native and non-native Ulmus pumila populations. Neobiota 15, 53–68. 14 Dec. 2012.
  51. ^ Geng, M. A. (1989). A provenance test with elm (Ulmus pumila L.) in China. Vol. 32. Silvae Genetica. pp. 37–44.
  52. ^ Dirr, M. (1975). Manual of Woody Landscape Plants. Champaign, Illinois: Stipes Publishing LLC. ISBN 0875630995.
  53. ^ Tree photo, Ulmus pumila 'Variegata', China; Plant Photo Bank of China, ppbc.iplant.cn
  54. ^ Leaves photo 1, Ulmus pumila 'Variegata', China; Plant Photo Bank of China, ppbc.iplant.cn
  55. ^ Leaves photo 2, Ulmus pumila 'Variegata', China; Plant Photo Bank of China, ppbc.iplant.cn
  56. ^ Leaves photo 3, Ulmus pumila 'Variegata', China; Plant Photo Bank of China, ppbc.iplant.cn
  57. ^ Green, Peter Shaw (1964). "Registration of cultivar names in Ulmus". Arnoldia. 24 (6–8). Arnold Arboretum, Harvard University: 41–80. Retrieved 16 February 2017.
  58. ^ Krüssmann, Gerd, Manual of Cultivated Broad-Leaved Trees & Shrubs (1984 vol. 3)
  59. ^ Baranov, A. L. (1962). On the economic use of wild plants in N. E. China. Quarterly Journal of the Taiwan Museum, 15 (122), 1962, 107–115.
  60. ^ Tolstoy, Leo, 'The Cossacks' and 'The Raid': a new translation by A.R. MacAndrew (New York, 1961)
  61. ^ Tolstoy, Leo, A Prisoner in the Caucasus and Other Stories, trans. Angus Roxburgh (Moscow, 1983)
  62. ^ de Roerich, G. (1931). Trails to Inmost Asia. Yale University Press
  63. ^ "List of plants in the {elm} collection". Brighton & Hove City Council. Retrieved 23 September 2016.
  64. ^ Herbarium specimen, sheet labelled U. pumila, from tree in Alemeya Agricultural University, Ethiopia; Botanical Collections Belgium, specimen BR0000020115166; botanicalcollections.be
  65. ^ Hedberg, I., Friis, I. & Persson, E. (2009). Flora of Ethiopia and Eritrea 1: 1-305; powo.science.kew.org
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