| Ulmus americana | |
|---|---|
| Details | |
| Cultivar | 'Washington' |
| Origin | USA |
The American Elm Ulmus americana cultivar 'Washington' is a tree of unknown derivation introduced by the U. S. National Park Service.
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The tree has been described as possibly having triploid chromosome levels (unusual for an American Elm), suggesting it may be a hybrid between the tetraploid American Elm and a diploid species. However, in view of a study performed by the United States National Arboretum in 2004 [1], this earlier supposition is likely to be erroneous; therefore, like the cultivar 'Jefferson' which was also once considered triploid, 'Washington' is probably tetraploid.
The tree is resistant to Dutch elm disease, but less so than other recent American Elm cultivars such as 'Valley Forge'. Like all other American Elm cultivars, it is also susceptible to Elm Yellows. No other specific information available, but the species generally is also moderately preferred for feeding and reproduction by the adult Elm Leaf Beetle Xanthogaleruca luteola [1] [2], and highly preferred for feeding by the Japanese Beetle Popillia japonica [2] [3] [4] in the USA. U. americana is the most susceptible of all the elms to verticillium wilt.[3]
Neither 'Washington' nor 'Jefferson' has been widely tested beyond Washington D.C.. The tree is not known to be in commerce, and is not known to be in cultivation beyond the USA.