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''Ulmus laevis'' Pall., called the European White Elm, Fluttering Elm, Spreading Elm, Stately Elm and Russian Elm, is a large deciduous tree native to Europe, from France〔Photographs of ''U. laevis'' (''L'Orme lisse'') in France: in the Forêt du Romersberg, Moselle, () (bottom of page), and near Walbourg, Bas-Rhin,() (top of page); Archive Krapo arboricole〕 northeast to southern Finland, east as far as the Urals, and southeast to Bulgaria and the Crimea; there is also a disjunct population in the Caucasus. Moreover, a small number of trees found in Spain is now considered a relict population rather than an introduction by man, and possibly the origin of the European population.〔Fuentes-Utrilla, P., Squirrell, J., Hollingsworth, P. M. & Gil, L. (2006). ''Ulmus laevis (Pallas) in the Iberian Peninsula. An introduced or relict tree species? New data from cpDNA analysis.'' Genetics Society, Ecological Genetics Group conference, University of Wales Aberystwyth 2006.〕 Endemic to alluvial forest, ''U. laevis'' is rarely encountered at elevations above 400 m.〔Girard, S. (2007). Dossier: L'orme: nouveaux espoirs? ''Forêt entreprise'' No. 175, Juillet 2007, Institut pour le developpement forestier, Paris.〕 Most commonly found along rivers such as the Volga and Danube, it is one of very few elms tolerant of prolonged waterlogged, anoxic ground conditions. Although not possessed of an innate genetic resistance to Dutch elm disease, the species is rarely infected in western Europe. The White Elm is allogamous and is most closely related to the American Elm ''U. americana''. ==Description== The tree is similar in stature to the Wych Elm, if rather less symmetric, with a looser branch structure and less neatly rounded crown. It typically reaches a height and breadth of > 30 m, with a trunk < 2 m d.b.h. The extensive shallow root system ultimately forms distinctive high buttresses around the base of the trunk. The leaves are deciduous, alternate, simple ovate with a markedly lop-sided base, < 10 cm long and < 7 cm broad, comparatively thin, often almost papery in texture and very translucent, smooth above with a downy underside. The apetalous wind-pollinated flowers appear before the leaves in early spring, produced in clusters of 15-30; they are 3–4 mm across on 20 mm long stems. In England, trees grown from seed flower in March, commencing at ages of between 7 and 12 years.〔Brookes, A. H. (2012). ''Disease-resistant elm cultivars, Butterfly Conservation trials report, 2nd revision, 2012.'' Butterfly Conservation, Hants & IoW Branch, England. ()〕 The fruit is a winged samara < 15 mm long by 10 mm broad with a ciliate margin, the single round 5 mm seed maturing in late spring. ''U. laevis'' sheds its leaves earlier in the autumn than other species of European elm. The tree is most reliably distinguished from other European elms by the long flower stems, and is most closely related to the American Elm ''U. americana'', from which it differs mainly in the irregular crown shape and frequent small sprout stems on the trunk and branches, features which also give the tree a winter silhouette; a useful diagnostic feature at this season.〔Bean, W. J. (1981). ''Trees and shrubs hardy in Great Britain'', 7th edition. Murray, London.〕 〔Elwes, H. J. & Henry, A. (1913). ''(The Trees of Great Britain & Ireland )''. Vol. VII. 1848–1929. Republished 2004 Cambridge University Press, ISBN 9781108069380〕 Although the species is protandrous, levels of self-pollination are high〔Hans, A. S. (1981). Compatibility and Crossability Studies in Ulmus. ''Silvae Genetica'' 30, 4 - 5 (1981).〕 The tree can grow very rapidly; where planted in persistently moist soil, trunk width of 13-year-old trees increased by 4 cm per annum at breast height (d.b.h.). 〔Brookes, A. H. (2015). ''Great Fontley Elm Trial, 2015 Report''. Butterfly Conservation, Lulworth, UK.〕 Image:Ulmus laevis root structure.jpg|Surface root structure exposed by bank erosion Image:UlmusBrettwurzel.jpg|''U. laevis'' buttresses Image:Wych elm flower.jpg|''U. laevis'' flowers; note long stems File:Ulmus laevis MHNT.BOT.2010.12.4.jpg|''U. laevis'' seeds Image:HW laevis leaf.jpg|''Ulmus laevis'' leaf Image:Ulmus laevis leaf, Nov..jpg|''U. laevis'' autumn colour 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ulmus laevis」の詳細全文を読む スポンサード リンク
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