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Ulmus minor

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Ulmus minor Mill., the field elm, is by far the most polymorphic of the European species, although its taxonomy remains a matter of contention. Its natural range is predominantly south European, extending to Asia Minor and Iran; its northern outposts are the Baltic islands of Öland and Gotland,[2] although it may have been introduced by humans. The tree's typical habitat is low-lying forest along the main rivers, growing in association with oak and ash, where it tolerates summer floods as well as droughts.[3]

Ulmus minor
Field elm, Blismes, Nièvre, France.
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Rosids
Order: Rosales
Family: Ulmaceae
Genus: Ulmus
Species:
U. minor
Binomial name
Ulmus minor
Distribution map
Synonyms
  • Ulmus araxina Takht.
  • Ulmus boissieri Grudz.
  • Ulmus campestre Anon.
  • Ulmus campestris L. var. australis Henry
  • Ulmus campestris L. var. dalmatica Baldacci
  • Ulmus campestris var. glabra Hartig, Planch., Aschers. & Graebn.
  • Ulmus campestris var. laevis Spach, Planch.
  • Ulmus campestris Huds. var. microphylla Boiss.
  • Ulmus canescens Melville
  • Ulmus carpinifolia Gled.
  • Ulmus coritana Melville
  • Ulmus densa Litv.
  • Ulmus foliacea Gilibert, Sarg.
  • Ulmus georgica Schchian
  • Ulmus glabra (not Huds.), Ley, Mill., Smith, Loudon, Rchb., Wilkomm, C. K. Schneid., Ley
  • Ulmus glabra Mill. var.pilifera Borbas
  • Ulmus grossheimii Takht.
  • Ulmus micrantha Kitt.
  • Ulmus microphylla Mill.
  • Ulmus microphylla Pers.
  • Ulmus minor subsp. minor Richens
  • Ulmus minor suberosa Moench, Rehder
  • Ulmus nemoralis Fraas
  • Ulmus nitens Moench
  • Ulmus pilifera Borbas
  • Ulmus procera Salisb.
  • Ulmus sparsa Dumrt.
  • Ulmus stricta (Aiton) Lindley
  • Ulmus stricta (Aiton) Lindley var goodyeri Melville
  • Ulmus tetrandra Sckk.
  • Ulmus tortuosa Host
  • Ulmus uzbekistanica Drob.
  • Ulmus wissotzkyi Kotov

Current treatment of the species owes much to Richens,[4] who noted (1983) that several varieties of field elm are distinguishable on the European mainland. Of these, he listed the small-leaved U. minor of France and Spain; the narrow-leaved U. minor of northern and central Italy; the densely hairy leaved U. minor of southern Italy and Greece; the U. minor with small-toothed leaves from the Balkans; the U. minor with large-toothed leaves from the Danube region; and the small-leaved U. minor from southern Russia and Ukraine.[5] As for British varieties, "the continental populations most closely related [to eastern English Field Elm] are in central Europe", while south-western forms were introduced from France.[6] He concluded, however, that owing to incomplete field-research at the time of writing, it was "not possible to present an overall breakdown of the European Field Elm into regional varieties".[7] The epithet 'red' elm was commonly used by British foresters, an allusion to the colour of the timber.[8]

Richens sank a number of British elms, notably English elm, as either subspecies or varieties of U. minor in 1968. However, Melville,[9] writing ten years later, identified five distinct species (including U. glabra in the count), several varieties and numerous complex hybrids. In 1992 Armstrong[10] identified no fewer than forty British species and microspecies. Clive Stace (1997) wrote of the British elms "The two-species (glabra and minor) concept of Richens is not sufficiently discriminating to be of taxonomic value". Nevertheless, it is Richens’ classification which has been the most commonly adopted in recent years, although it is not used in Flora Europaea.[11][12]

In 2009 Dr Max Coleman of the Royal Botanic Garden, Edinburgh wrote: "The advent of DNA fingerprinting has shed considerable light on the question. A number of studies have now shown that the distinctive forms Melville elevated to species and Richens lumped together as field elm are single clones, all genetically identical, which have been propagated by vegetative means such as cuttings or root suckers. This means that enigmatic British elms such as Plot elm and English elm have been shown to be single clones of field elm. Although Richens did not have the evidence to prove it, he was correct in recognising a series of clones and grouping them together as a variable species."[13]

It is hoped that analysis of molecular markers will ultimately eliminate the taxonomic confusion.

Description

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The tree typically grows to < 30 m (98 ft) and bears a rounded crown.[14] The bark of the trunk is rough, furrowed lightly in older trees to form a block pattern. Young branchlets occasionally have corky wings. The shoots are slender compared with those of wych elm. The leaves are smaller than those of the other European species, hence the specific epithet minor, however they can vary greatly according to the maturity of the tree. Leaves on juvenile growth (suckers, seedlings etc.) are coarse and pubescent, whereas those on mature growth are generally smooth, though remaining highly variable in form; there are generally fewer than 12 pairs of side veins.[15] A common characteristic is the presence of minute black glands along the leaf veins, detectable with the aid of a magnifying glass.[3] The samarae are oval or obovate, glabrous, 12–15 mm (15⁄32–19⁄32 in) long, notched at the top, with the seed close to the notch.[16] Ulmus minor in France generally begins to flower and fruit when aged 10 years.[17]

The species readily produces suckers from roots and stumps, even after devastation by Dutch elm disease; consequently genetic resources are not considered endangered.[18]

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    Typical U. minor form, East Coker, UK (2008)
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    U. minor inflorescence
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    U. minor samarae
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    U. minor seedlings
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    U. minor foliage
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    Leaf and 1 Euro coin
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    Root-suckers spreading around a field elm
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    Bark of Stapleford elm, UK
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    Bark of U. minor, Bulgaria

Pests and diseases

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The species has a hugely variable reaction to Dutch elm disease (DED), including all the fashionable pre-20th century plantsman's clones (see Subspecies and varieties). However, field elm is genetically highly variable; Italian specimens when inoculated with the pathogen displayed between 15 and 100% dieback and between 70 and 100% wilting, whereas with trees tested in Spain, the variability ranged from 5 to 100% dieback, and 20 to 95% wilting.[19] In 2013 researchers at the Universidad Politėcnica de Madrid announced the discovery and cloning of trees in Spain with levels of resistance greater than 'Sapporo Autumn Gold'[20] (see Cultivation).

Tolerance of elm yellows (phloem necrosis) is generally good, U. minor exhibiting symptoms such as the 'witch's broom' only sporadically throughout Italy, including Sicily and Sardinia, however the disease was often locally common within the species in France, including Paris.[21]

Cultivation

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U. minor in general and a number of clones in particular (see 'Cultivars' below) were once commonly cultivated across Europe in town and country, but owing to its susceptibility to Dutch elm disease, U. minor is now uncommon in cultivation. However, in an ongoing project that began in the 1990s, several thousand surviving field elms have been tested for innate resistance by national research institutes in the EU, with a view to returning field elm to cultivation.[19] Results from Spain (2013), for example, confirm that a very small number of surviving field elms (about 0.5% of those tested) appear to have comparatively high levels of tolerance of the disease, and it is hoped that a controlled crossing of the best of these will produce resistant Ulmus minor hybrids for cultivation.[22]

In the UK, despite its late leaf-flush in the north and its suckering habits, continental U. minor was occasionally planted as an ornamental urban tree. Augustine Henry wrote in 1913 that the U. minor planted in parks in Scotland were of French origin.[23] More recently U. minor seed was imported to the UK from Italy.[24] There are mature survivors in Edinburgh that are not the common U. minor cultivars (2015).[25]

U. minor has been introduced to the southern hemisphere, notably Australasia and Argentina.[26]

Notable trees

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U. minor can live to a great age. An ancient field elm stood until recently in the village square of Metaxades, Thrace, Greece. Having abandoned their original village in 1286 after cholera outbreaks, the villagers re-founded it in the hills where a young elm was growing beside a spring. An elm (reputedly the original) and the fountain were the focal-point of the village until the late 20th century.[27] The tallest recorded field elms in Greece were two specimens planted in 1650 beside the newly built church of the Archangels Michael and Gabriel, in Omali Voiou (Oμαλή Bοΐου) near Siatista, which, despite being open-grown trees, attained a height of 40 metres by the mid-20th century.[28] The immemorial elm opposite the village square of Aidona in Thessaly, Greece[29][30] which has been "listed" as a national "Monument of Nature",[31] lost its crown in a recent storm (2009) and has now been pollarded; it is regenerating vigorously. A rare example of a centuries-old field elm that retains its heartwood and crown is the 360-year-old specimen in the village square of Strinylas, Corfu.[32][33][34]

A tree said to be of similar age (200 cm d.b.h.) still stands (2013) in the city of Sliven, Bulgaria; other veterans are said to survive in the village of Samuilovo, 7 km from Sliven.[35][36][37]

In France, a tree reputedly over 650 years old survived in the centre of Biscarrosse south of Bordeaux until the summer of 2010, when it finally succumbed to Dutch elm disease.[38] Another veteran with a 6-metre girth survives at Bettange, France, close to the Belgian border, reputedly planted in 1593.[39] Other wrecks include 'l'ormeau de Sully' in Villesèquelande near Carcassonne,[40] "a magnificent tree supported by three metal props", said to have been planted in the early 17th C by the Duc de Sully,[41]

A tree approximately 400 years old and 5.55 metres in girth grows in the town of Mergozzo in Piedmont, Italy. 'L'olmo di Mergozzo', like its French counterparts 'l'orme de Biscarosse' and 'l’orme de Bettange', is hollowed out by age, its life prolonged by lopping, while in Spain the elm in the Plaza del Olmo ("Elm square" in Spanish) in Navajas, Valencia, is 6.3 metres in girth; planted in 1636 it features on the town crest.[42]

In England, large specimens once identified as U. minor subsp. minor, the narrow- or smooth-leafed elm, were once commonplace in the eastern counties before the advent of DED. The largest recorded tree in the UK grew at Great Amwell, Hertfordshire, measuring 40 m in height and 228 cm d.b.h. in 1911.[43] Another famous specimen was the great elm that towered above its two siblings at the bottom of Long Melford Green, Long Melford, Suffolk,[44] till the group succumbed to disease in 1978. The three "were survivors of a former clone of at least nine elms, one dating from 1757".[45] The Long Melford elms were painted in 1940 by the watercolourist S. R. Badmin in his 'Long Melford Green on a Frosty Morning', now in the Victoria and Albert Museum.[46] The largest known surviving trees in England are at East Coker, Somerset (30 m high, 95 cm d.b.h.), Termitts Farm near Hatfield Peverel, Essex (25 m high, 145 d.b.h.), and Melchbourne, Bedfordshire, (147 cm d.b.h.).[47]

Subspecies, varieties, and former species sunk as U. minor

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England

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The name Ulmus minor subsp. minor was used by R. H. Richens[48] for field elm that was not English elm, Cornish elm, Plot elm or Guernsey elm. Many publications, however, continue to use plain Ulmus minor for undifferentiated field elm; indeed Dr Max Coleman of Royal Botanic Garden Edinburgh argued in his 2002 paper 'British Elms' that there was no clear distinction between species and subspecies.[49] Some authorities, among them Richens[50] and Coleman,[13] include English elm among varieties of field elm, Richens calling English elm U. minor var. vulgaris. Richens sank as undifferentiated U. minor certain local English forms such as U. minor 'Goodyeri', U. minor 'Hunnybunii', U. minor 'Sowerbyi', and U. minor 'Coritana'.[citation needed]

Eurasia

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Henry's Ulmus nitens var. italica, 'Mediterranean Elm' (1913), distinguished by its 14 to 18 pairs of leaf-veins,[51] was accepted, despite the wide source-area claimed for it ("Italy, Spain, Portugal and Algeria"), as U. carpinifolia var. italica Henry, by Krüssman (1984), who included a photograph of a specimen in Gisselfeld Park, Denmark.[52] Bean (1988), however, considered it "a variety of rather dubious standing",[53] and it was ignored by Richens (1983).

U. canescens Melville and U. boissieri Grudz. were both sunk as U. minor by Richens.[54] The former is found throughout the eastern Mediterranean, including Palestine and Israel, and is distinguished by its leaves, densely downy on the underside when mature.[55][56] The latter is a little-known tree found in Iran, in the Zagros forests and the Kerman / Kermanshah area.[57] Green and Richens also sank U. minor var. suberosa (Moench) Rehder - the so-called 'Cork-barked elm', korkulme (Germany) or wiąz korkowa (Poland), as a genetically random, maritime or juvenile form of U. minor, insufficiently differentiated to merit varietal status, its name a relic of taxonomic conservatism.[58][59]

Cultivars

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Numerous cultivars have been raised in Europe since the 18th century, although many are now probably either extinct owing to the ravages of Dutch elm disease, or survive unrecognized in sucker form:

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    Bonsai field elm

Hybrids

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The tree's natural range generously overlaps that of wych elm Ulmus glabra to the north, and readily hybridizes with it to produce the so-called 'Dutch elm' Ulmus × hollandica.[60]

In Spain and Italy Ulmus minor has naturally hybridized with Siberian elm U. pumila. In Spain U. pumila was introduced in the 16th century and has since spread widely, contributing to conservation concerns for U. minor.[61] In Italy U. pumila was introduced in the 1930s; research is ongoing into the extent of its hybridisation with U. minor.[62] The resulting hybrid has not yet been given a formal botanical name, though there are cultivated forms such as 'Recerta' and 'Fiorente' (see 'Hybrid cultivars').

Hybrid cultivars

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U. minor hybridises naturally with U. glabra, producing elms of the Ulmus × hollandica group, from which there have arisen a number of cultivars:

The tree has featured strongly in artificial hybridization experiments in Europe and to a lesser extent in the United States. The hybrid Ulmus davidiana var. japonica × U. minor was raised at the Arnold Arboretum before 1924.[63] Most of the European research was based at Wageningen in the Netherlands until 1992, whence a number of hybrid cultivars have been commercially released since 1960. The earlier trees were raised in response to the initial Dutch elm disease pandemic that afflicted Europe after the First World War, and were to prove vulnerable to the much more virulent strain of the disease that arrived in the late 1960s. However, further research eventually produced several trees highly resistant to disease which were released after 1989.[64]

In art

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The elms by Willy Lott's Cottage and Flatford Mill, Suffolk, in Constable's paintings and drawings were, according to Richens, "smooth-leaved elm" (U. minor),[65] though the hedgerow elms in his Dedham Vale and East Bergholt landscape-paintings and drawings were otherwise "most probably East Anglian hybrid elms ... such as still grow in the same hedges".[66]

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    Field elm beside Willy Lott's Cottage in Constable's The Hay Wain (1821)
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    The same, in Constable's Flatford Lock, Christchurch Mansion, Ipswich

Accessions

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North America

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Europe

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Australasia

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Nurseries

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North America

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None known

Europe

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References

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  1. ^ Barstow, M.; Rivers, M.C.; Harvey-Brown, Y. (2017). "Ulmus minor". IUCN Red List of Threatened Species. 2017: e.T19218731A69047375. doi:10.2305/IUCN.UK.2017-3.RLTS.T19218731A69047375.en. Retrieved 21 July 2023.
  2. ^ Ulmus minor in Gotland, Sweden: ulmen-handbuch.de/handbuch/ulmus
  3. ^ a b Heybroek, H. M., Goudzwaard, L, Kaljee, H. (2009). Iep of olm, karakterboom van de Lage Landen (:Elm, a tree with character of the Low Countries). KNNV, Uitgeverij. ISBN 9789050112819
  4. ^ Richens, R. H. (1968). "The correct designation of the European field elms". Feddes Repertorium. 79 (1–2): 1–2. doi:10.1002/fedr.19680790102.
  5. ^ Richens, R. H., Elm (Cambridge 1983), p.18
  6. ^ Richens, R. H., Elm (Cambridge 1983), p.21
  7. ^ Richens, R. H., Elm (Cambridge 1983), p.88
  8. ^ Edlin, H. L. (1947). British Woodland Trees,  p.26. 3rd. edition. London: B. T. Batsford Ltd.
  9. ^ Melville, R (1978). "On the discrimination of species in hybrid swarms with special reference to Ulmus and the nomenclature of U. minor (Mill.) and U. carpinifolia (Gled.)". Taxon. 27: 345–351. doi:10.2307/1220370. JSTOR 1220370.
  10. ^ Armstrong, J. V.; Sell, P. D. (1996). "A revision of the British elms (Ulmus L., Ulmaceae): the historical background". Botanical Journal of the Linnean Society. 120: 39–50. doi:10.1111/j.1095-8339.1996.tb00478.x. Retrieved 26 October 2017.
  11. ^ Flora Europaea
  12. ^ Stace, C. A. (1997). New Flora of the British Isles. 2nd edition. Cambridge University Press.
  13. ^ a b Max Coleman, ed.: Wych Elm (Royal Botanic Garden Edinburgh publication, 2009; ISBN 978-1-906129-21-7); p. 22
  14. ^ Photographs of Ulmus minor in France (L’orme de Martailly-lès-Brancion), krapooarboricole.wordpress.com [1] ; in Portugal, 1.bp.blogspot.com [2].
  15. ^ "Herbarium specimen - L.4222648". Botany catalogues. Naturalis Biodiversity Center. Labelled Ulmus carpinifolia Gled., Pont du Gard, France, 1981
  16. ^ Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London. [3]
  17. ^ Brookes, A. H. (2020). Great Fontley Elm Trial, 2020 Report. Butterfly Conservation, Lulworth, England.
  18. ^ "European elms (Ulmus SPP.) genetic resources conservation strategy". Archived from the original on 2003-09-29.
  19. ^ a b Solla, A., Bohnens, J., Collin, E., Diamandis, S., Franke, A., Gil, L., Burón, M., Santini, A., Mittempergher, L., Pinon, J., Vanden Broeck, A. (2005). Screening European elms for resistance to Ophiostoma novo-ulmi. Forest Science, 51(2) 2005 134-141.
  20. ^ Martín, JA; Solla, A; Venturas, M; Collada, C; Domínguez, J; Miranda, E; Fuentes, P; Burón, M; Iglesias, S; Gil, L (2015-04-01). "Seven Ulmus minor clones tolerant to Ophiostoma novo-ulmi registered as forest reproductive material in Spain". IForest - Biogeosciences and Forestry. 8 (2). Italian Society of Sivilculture and Forest Ecology (SISEF): 172–180. doi:10.3832/ifor1224-008. ISSN 1971-7458.
  21. ^ Mittempergher, L. (2000). Elm Yellows in Europe. in Dunn, C.P., (ed.): The Elms, Breeding, Conservation, & Disease Management. 104-105. Boston: Kluwer Academuic Publishing.
  22. ^ ‘Spanish Clones’ (Oct. 2013) resistantelms.co.uk
  23. ^ Elwes, Henry John; Henry, Augustine (1913). The Trees of Great Britain and Ireland, Volume VII. Edinburgh. p. 1897–8. ISBN 9781108069380.{{cite book}}: CS1 maint: location missing publisher (link)
  24. ^ E. E. Kemp (Curator, Royal Botanic Garden Edinburgh 1950-71) in After the Elm, eds. Clouston & Stansfield, (London, 1979)
  25. ^ Boswall Rd [two]; corner of Abbey Mount and Regent Rd; News Steps; Carlton Terrace Brae; Links Place; Seafield Place. Verified by samarae, leaves, suckering habit, form, and late leaf-flush; trees all on Streetview.
  26. ^ 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,  p.45. Abstract.
  27. ^ "Η ιστορία των Μεταξάδων". Archived from the original on 2011-07-21. Retrieved 2010-12-15.
  28. ^ The elms of Omali Voiou: «Oι εκκλησίες της Oμαλής Bοΐου» [:The Churches of Omali Voiou], photograph 7 (p.25): www.scribd.com [4]
  29. ^ Summer photograph of the centuries-old Aidona elm: sites.google.com
  30. ^ Winter photograph of Aidona elm: nikos-manitarielassonas, photograph 3
  31. ^ Διατηρητέα Μνημεία της Φύσεως αριθ.36 (:Listed Monuments of Nature, No. 36): https://web.archive.org/web/20080616173320/http://users.otenet.gr/~theonik/peribal/esthitik.htm
  32. ^ The elm in Strinylas, Corfu: greeka.com
  33. ^ The elm in Strinylas, Corfu: greeka.com/ionian/corfu/corfu-villages/strinilas-corfu.htm; https://web.archive.org/web/20011224222535/http://www.manfred-peters.de/Titel_Korfu_Tip_Nord.htm
  34. ^ The elm in Strinylas, Corfu: static.panoramio.com
  35. ^ European Tree of the Year 2013, facebook.com/photo.php?fbid=655819444441287&set=a.366730233350211.84042.112234408799796&type=1&relevant_count=1&ref=nf
  36. ^ Sliven Elm in autumn (photo: Rositsa Mitkova), panoramio.com
  37. ^ "'The Sliven elm-tree runs for European Tree of the Year', bnr.bg". Archived from the original on 2014-01-11. Retrieved 2014-01-11.
  38. ^ krapooarboricole.wordpress.com, [5] [6] [7]
  39. ^ arbresvenerables.free.fr "Venerable Trees of the Earth - France". Archived from the original on 2008-05-02. Retrieved 2015-02-05., krapooarboricole.wordpress.com [8]
  40. ^ L'Ormeau de Sully, Villesèquelande, panoramio.com
  41. ^ sullystrees.weebly.com/list-of-trees-by-french-departements.html
  42. ^ Ayuntamiento de Navajas, Historia y patrimonio
  43. ^ Elwes, Henry John; Henry, Augustine (1913). The Trees of Great Britain and Ireland, Volume VII. Edinburgh. p. 1899. ISBN 9781108069380. Retrieved 15 December 2021.{{cite book}}: CS1 maint: location missing publisher (link)
  44. ^ Photograph of the great elms on Long Melford Green (Francis Frith Collection, images.francisfrith.com) [9]
  45. ^ Photograph, plate XXI(h), in Oliver Rackham, A History of the Countryside (London, 1986),  p.236.
  46. ^ S. R. Badmin's 'Long Melford Green on a Frosty Morning', Victoria and Albert Museum [10]
  47. ^ Tree Register Of the British Isles (TROBI)
  48. ^ Richens, R. H., Elm (Cambridge 1983),  p.280
  49. ^ Coleman, M (2002). "British elms". British Wildlife. 13 (6): 390–395.
  50. ^ Richens, R. H., Elm (Cambridge, 1983)
  51. ^ Elwes, Henry John; Henry, Augustine (1913). The Trees of Great Britain and Ireland, Volume VII. Edinburgh. p. 1892–3. ISBN 9781108069380.{{cite book}}: CS1 maint: location missing publisher (link)
  52. ^ Krüssman, Gerd, Manual of Cultivated Broad-Leaved Trees & Shrubs (1984 vol. 3), pl.144
  53. ^ Bean, W. J., Trees and shrubs hardy in Great Britain (1988) beanstreesandshrubs.org
  54. ^ Richens, R.H. (1983). Elm. Cambridge University Press. p. 279 §82. ISBN 9780521249164.
  55. ^ Melville, R. (1957). Ulmus canescens: an eastern Mediterranean elm. Kew Bulletin: 499–502, 1957
  56. ^ Flora of Israel and adjacent areas
  57. ^ Grudzinskaya, I. A. (1977). "The new elm species - Ulmus boissieri. New species of Ulmaceae from Iran" (PDF). Botanicheskii Zhurnal (in Russian). 62 (6). St. Petersburg, Russia: Komarov Botanical Institute: 856. Archived (PDF) from the original on 21 July 2023.
  58. ^ Green, Peter Shaw (1964). "Registration of cultivar names in Ulmus". Arnoldia. 24 (6–8). Arnold Arboretum, Harvard University: 41–80. Retrieved 16 February 2017.
  59. ^ Richens, R. H., Elm (Cambridge 1983), p.83, p. 278
  60. ^ Richens, R. H., Elm (Cambridge, 1983), p. 95, 233
  61. ^ Miguel (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.
  62. ^ 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.
  63. ^ The Morton Arboretum Living Collection, Ulmus list, quercus.mortonarb.org
  64. ^ Heybroek, H.M. (1993). "The Dutch Elm Breeding Program". In Sticklen, Mariam B.; Sherald, James L. (eds.). Dutch Elm Disease Research. New York, USA: Springer-Verlag. pp. 16–25. ISBN 978-1-4615-6874-2. Retrieved 26 October 2017.
  65. ^ Richens, R. H., Elm (Cambridge 1983), p.173; p.293, note 26
  66. ^ Richens, R. H., Elm (Cambridge 1983), p.166, 179
  67. ^ Royal Botanic Garden Edinburgh. (2017). List of Living Accessions: Ulmus [11]
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