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American elm is a vase-shaped, medium to large, deciduous tree. [4] The tree can grow to greater than 30 m in height, and is distinguished by its dense, symmetrical, upright form and dark green foliage, ultimately forming a broad umbrella crown. Crotch angles can be acute, with considerable bark inclusion which can later lead to branch breakages.
The Field Elm cultivar Ulmus minor 'Christine Buisman' was the first cultivar released by the Dutch elm breeding programme, initiated in response to the less virulent form of Dutch elm disease (DED), Ophiostoma ulmi, which afflicted Europe's elms after the First World War. [1] '
The American elm is a deciduous tree which, under ideal conditions, can grow to heights of 21 to 35 meters (69 to 115 feet). [3] The trunk may have a diameter at breast height (dbh) of more than 1.2 m (4 ft), supporting a high, spreading umbrella-like canopy.
Ulmus thomasii, the rock elm [3] or cork elm (or orme liège in Québec), is a deciduous tree native primarily to the Midwestern United States. The tree ranges from southern Ontario and Quebec , south to Tennessee , west to northeastern Kansas , and north to Minnesota .
Ulmus 'Frontier' is an American hybrid cultivar, a United States National Arboretum introduction (NA 55393) derived from a crossing of the European Field Elm Ulmus minor (female parent) with the Chinese Elm Ulmus parvifolia in 1971. Released in 1990, the tree is a rare example of the hybridization of spring- and autumn-flowering elms.
Ulmus 'Patriot' is a hybrid cultivar raised by the United States National Arboretum in 1980. Derived from a crossing of the American hybrid 'Urban' (female parent) with the Wilson's Elm (now treated as Japanese Elm U. davidiana var. japonica) cultivar 'Prospector', 'Patriot' was released to commerce, free of patent restrictions, in 1993.
Ulmus 'Morton Plainsman' (selling name Vanguard) is a hybrid cultivar raised by the Morton Arboretum from a crossing of Siberian Elm (female parent) and a Japanese Elm grown from openly pollinated seed donated by the Agriculture Canada Research Station at Morden, Manitoba.
Christine Johanna Buisman (Dutch pronunciation: [krɪsˈtinə joːˈɦɑnaː ˈbœysmɑn]; 22 March 1900 – 27 March 1936) was a Dutch phytopathologist who dedicated her short career to the research of Dutch elm disease and the selection of resistant elm seedlings.