| 0 | PI 635109 | 'Jefferson' | Ulmus americana L. | Maryland, United States | NC7 | | Not Available | 2004 | DEVELOPED | | | | | | Cultivar | Selected from approximately 600 elms planted on the National Mall in Washington D.C. Triploid selection released jointly by the U.S. National Arboretum and the National Park Service in 2004 because of its disease tolerance and exceptional horticultural characteristics. In experiments conducted in the District of Columbia and at Glenn Dale, Maryland, rooted cuttings have demonstrated high levels of tolerance to both species of the fungus which causes Dutch elm disease. Tolerance of this clone to Dutch elm disease is characterized by a significantly lower extent of foliar symptoms and crown dieback after fungal inoculation, compared to other American elm selections and seedlings. Although not completely immune to the disease, it has an unusually high level of disease tolerance and will contribute to the diversity of elm selections now becoming available in the nursery and landscape industries. A diversity of American elm cultivars will help sustain the species as it begins to regain its stature in the urban forest. Distinguished by dark green leaves which develop earlier in the spring and are retained later in the fall than surrounding American elms. The parent tree is approximately 70 years old (90 cm DBH, 20.6 m tall) and has an expansive umbrella-shaped crown. Branch unions are broad and U-shaped compared to the narrow V unions often found in other American elm trees. The bark is smooth, light to reddish gray in young trees becoming dark gray and fissured in older trees. Summer leaves average 106 mm long by 59 mm wide and are dark green, turning yellow in the autumn. In adaptability trials, it has grown well in the District of Columbia, Maryland, Minnesota, Missouri, New Jersey, Oklahoma, Oregon, and Tennessee, and can be considered adaptable from USDA Zones 4 through 7. Readily propagated by softwood cuttings. Using conventional techniques, 90% of the cuttings collected in mid-May in the District of Columbia usually root within 10 weeks. Excellent choice for planting in urban and suburban sites, large yards, and recreational and industrial parks. It will make a good street tree where there is a wide tree lawn, and where a high arching effect is desired. Its combination of Dutch elm disease tolerance, widespread adaptability, and umbrella-shaped crown will fill important needs of the American public. | 1662748 | PI 635109 |
| 1 | PI 590997 | 'Valley Forge' | Ulmus americana L. | District of Columbia, United States | NC7 |  | | 1995 | DEVELOPED | | | | | | Cultivar | Introduced by the U.S. National Arboretum in 1995. Tetraploid selected by A. M. Townsend and L. R. Schreiber. Unusually high levels of tolerance to both aggressive and non-aggressive strains of the fungus causing Dutch elm disease. Superior horticultural characteristics. Upright, arching, broad vase-shaped branching structure with full, dense canopy of leaves. Propagules off original parent tree (suspected origin is Nebraska) are 7.9 meters tall with average crown spread of 9.1 meters after 12 growing seasons. Summer leaves average 119 mm long x 74 mm wide and are green but gradually turn yellow in autumn. Bark divided into grayish, flat-topped ridges, separated by roughly diamond-shaped fissures, and is typical of the species. In adaptability trials, performed well in Ohio, Maryland, and the District of Columbia. Adaptable from USDA Zone 5 to 7. Easy to propagate. Excellent for planting in urban and suburban sites, large yards, and recreational and industrial parks. Good street trees where there is wide tree lawn, and where high arching effect is desired. | 1493695 | PI 590997 |
| 2 | PI 590998 | 'New Harmony' | Ulmus americana L. | District of Columbia, United States | NC7 | | Not Available | 1995 | DEVELOPED | | | | | | Cultivar | Introduced by the U.S. National Arboretum in 1995. Tetraploid selected by A. M. Townsend and L. R. Schreiber. Unusually high levels of disease tolerance to both aggressive and non-aggressive strains of the fungus causing Dutch elm disease. Superior horticultural characteristics. Broadly, vase-shaped crown, with main trunk dividing about 9 meters from the ground into several erect limbs which strongly arch above and which terminate in numerous slender, often drooping branchlets. Parent tree (origin near Springfield, Ohio) is 20.7 meters tall, with an average crown spread of 21.9 meters. Leaves average 107 mm long and 63 mm wide, and turn yellow in autumn. Bark is typical of species. Grows well in Georgia, Maryland, Minnesota, New Jersey, Ohio, Oklahoma, Pennsylvania, and Tennessee. Adaptable from USDA Zone 5 to 7, with possible cold hardiness into Zone 4. Easy to propagate. Excellent for planting in urban and suburban sites, large yards, and recreational and industrial parks. Good street trees where there is wide tree lawn, and where high arching effect is desired. | 1493745 | PI 590998 |