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Testing in laboratory conditions by the United States Department of Agriculture from 1992 to 1993 revealed that 'Princeton' had some resistance to Dutch elm disease (DED), [6] [7] [8] although the original Princeton elm, which grew in Princeton Cemetery and was estimated to be over 150 years old, was felled in April 2005 after suffering 60 percent dieback, attributed by some accounts to Dutch ...
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.
The starting-points for List of elm cultivars, hybrids and hybrid cultivars were fourfold: (1) Green's 'Registration of Cultivar Names in Ulmus ' (1964), [1] based on the contemporary nomenclature of elm species and wild hybrids; (2) Krüssmann's confirmation or correction of cultivar-names in his monumental Handbuch der Laubgehölze (1976); [2] (3) Heybroek's table of Netherlands research ...
It was steadily weakened by viruses in Europe and had all but disappeared by the 1940s. However, the disease had a much greater and longer-lasting impact in North America, owing to the greater susceptibility of the American elm, Ulmus americana, which masked the emergence of the second, far more virulent strain of the disease Ophiostoma novo-ulmi.
The American elm cultivar Ulmus americana 'American Liberty' is in fact a group of six genetically distinct cultivars under a single name, although they are superficially similar. [1] The Liberty elm is reportedly suitable for street planting, being tolerant of de-icing salts and air pollution.
The perfect apetalous wind-pollinated flowers are vernal, appearing before the leaves unfold, born in long-pedicelled fascicles of 3 or 4. The fruit is a samara maturing in the spring as the leaves unfold; about 12 mm (½ inch) long, oval to oblong-obovate, deeply notched at apex, margin ciliate with smooth surfaces.
The American Elm cultivar Ulmus americana 'Independence' was raised by Eugene B. Smalley and Donald T. Lester at the University of Wisconsin–Madison from a crossing of the American Elm cultivar Moline and American Elm clone W-185-21, to become one of the six clones forming the American Liberty series, and the only one to be patented (U. S. Plant Patent 6227, 1988).
The American Elm cultivar Ulmus americana 'Lake City' is a semi-fastigiate form cloned in the early 1920s from a ten-year old seedling found growing outside the Lutheran parsonage, Lake City, Minnesota, and released by the Lake City Nurseries there in 1931.