|Hybrid parentage||U. minor × U. parvifolia|
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. Tested in the US National Elm Trial coordinated by Colorado State University, 'Frontier' averaged a survival rate of 74% after 10 years.
'Frontier' develops a vase or pyramidal shape, with glossy green foliage turning, unusually for elms, to burgundy in autumn. m. The tree is autumn-flowering but rarely does so, and has not produced seed.The twigs are pubescent. Slow growing, the ultimate height of the tree has yet to be determined, but should be > 15
'Frontier' has a good resistance to Dutch elm disease, rated 4 out of 5,but tolerance of Elm Yellows from grafts in the United States was found to be poor. However, no mortalities are known to have occurred from the latter disease in the field, the cultivar not known to be vulnerable to infection through natural means. The tree can be heavily to severely damaged by the Elm Leaf Beetle Xanthogaleruca luteola , although it fared better than most of the cultivars assessed at U C Davis, suffering little more than 10% foliar damage. Although susceptible to attack by Japanese Beetle, it is far less seriously affected than most hybrid cultivars available in the United States.
In trials in eastern Arizona , 'Frontier' and another American hybrid, 'Regal', were found to have the highest tolerance of the hot and arid climate, notably exhibiting minimal leaf scorch. However, 'Frontier' is known to have sustained winter damage where planted in the Great Plains . This failing was repeated in the elm trials conducted by the University of Minnesota, although the tree often recovered the following year. It was also criticized for its form and integrity, considered "unsuitable" for urban forestry.'Frontier' fared better in 10-year trials at Atherton, California, to evaluate replacements for Californian elms lost to disease: "Strong structure, rapid growth rate, attractive leaf color in spring and fall, and relatively low pruning requirement suggest that Frontier has promise...", although the tree again proved only moderately tolerant of elm leaf beetles.
'Frontier' has had a limited introduction to Europe,where it is largely restricted to arboreta and elm collections; it also featured in trials in New Zealand during the 1990s at the Hortresearch station, Palmerston North.
Ulmus 'New Horizon' is an American hybrid cultivar raised by the Wisconsin Alumni Research Foundation (WARF), from a crossing of the Japanese Elm clone W43-8 = 'Reseda' with Siberian Elm clone W426 grown from seed collected from a street tree at Yankton, South Dakota. Tested in the US National Elm Trial coordinated by Colorado State University, 'New Horizon' averaged a survival rate of 74% after 10 years.'New Horizon' was patented in the US in 1994, while in Europe, it is marketed as one of the 'Resista' elms protected under E U breeders' rights.
Ulmus 'Homestead' is an American hybrid elm cultivar raised by Alden Townsend of the United States National Arboretum at the Nursery Crops Laboratory in Delaware, Ohio. The cultivar arose from a 1970 crossing of the Siberian Elm Ulmus pumila with the hybrid N 215, the latter grown from seed sent in 1960 to the University of Wisconsin-Madison elm breeding team by Hans Heybroek of the De Dorschkamp Research Institute in the Netherlands. Tested in the US National Elm Trial coordinated by Colorado State University, 'Homestead' averaged a survival rate of 85% after 10 years. 'Homestead' was released to commerce without patent restrictions in 1984.
The hybrid elm cultivar Ulmus × hollandica 'Pioneer' is an American clone arising from the crossing of two European species, Wych Elm U. glabra and Field Elm U. minor. Raised by the USDA station at Delaware, Ohio, in 1971, 'Pioneer' was released to commerce in 1983.
Ulmus 'Regal' is an American hybrid elm cultivar developed by the University of Wisconsin–Madison and released in 1983. 'Regal' was derived from seeds arising from the crossing of the Dutch hybrid clones 'Commelin' and '215' sent in 1960 by Hans M. Heybroek of the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen, Netherlands.
Ulmus 'Sapporo Autumn Gold' is one of the most commercially successful hybrid elm cultivars ever marketed, widely planted across North America and western Europe, although it has now been largely supplanted by more recent introductions. Arising from a chance crossing of the Japanese elm and Siberian elm, seed was sent in 1958 by Prof. Nobuku Takahashi and his colleagues at the Sapporo Botanical Garden of Hokkaido University, Sapporo, to Eugene Smalley at the University of Wisconsin–Madison. The patent issued in 1975 has expired, and there are now no propagation restrictions.
Ulmus 'Urban' is an American hybrid elm cultivar selected from the progeny of a controlled crossing of the Siberian Elm Ulmus pumila with the Dutch clone '148' in 1958 by Toru Arisumi of the USDA at Columbus, Ohio. Clone '148' had been sent to the US from the Netherlands in 1952 by Johanna Went, leader of the elm research team at the Willie Commelin Scholten Phytopathology Laboratory in Baarn.
Ulmus 'Morton' is an elm cultivar cloned from a putative intraspecific hybrid planted at the Morton Arboretum in 1924, which itself originated as seed collected from a tree at the Arnold Arboretum in Massachusetts. Although this tree was originally identified as Ulmus crassifolia, it is now believed to have been a hybrid of the Japanese elm and Wilson's elm. Accolade has proven to be the most successful cultivar tested in the US National Elm Trial, averaging a survival rate of 92.5% overall.
Ulmus 'Morton Glossy' is a hybrid cultivar raised by the Morton Arboretum, Illinois. Originally named 'Charisma' until it was realized that name had already been registered for another plant, the tree was derived from a crossing of two other hybrid cultivars grown at the Morton: Accolade and Vanguard. Tested in the US National Elm Trial coordinated by Colorado State University, Triumph averaged a survival rate of 86% after 10 years. Triumph was introduced to the UK in 2006 by the Frank P. Matthews nursery in Worcestershire.
Ulmus 'Morton Plainsman' is a hybrid cultivar raised by the Morton Arboretum from a crossing of Siberian Elm and a Japanese Elm grown from openly pollinated seed donated by the Agriculture Canada Research Station at Morden, Manitoba. Tested in the US National Elm Trial coordinated by Colorado State University, Vanguard averaged a survival rate of 78% after 10 years.
Ulmus 'Morton Red Tip' is a hybrid cultivar raised by the Morton Arboretum from an open pollination of Ulmus 'Morton'. The tree has occasionally been reported as a hybrid of Accolade with the Siberian Elm Ulmus pumila, an error probably owing to the commercial propagation of the tree by grafting onto U. pumila rootstocks. Tested in the US National Elm Trial coordinated by Colorado State University, Danada Charm averaged a survival rate of 77.5% after 10 years.
The American Elm cultivar Ulmus americana 'Princeton' was originally selected in 1922 by New Jersey nurseryman William Flemer of Princeton Nurseries for its aesthetic merit. 'Princeton' was later found to have a moderate resistance to Dutch elm disease (DED).
The American Elm cultivar Ulmus americana 'Valley Forge' was raised by the Agricultural Research Service in Maryland. The tree was released to wholesale nurseries without patent restrictions by the U. S. National Arboretum in 1995 after proving to have a high resistance to Dutch elm disease. 'Valley Forge' proved only moderately successful in the US National Elm Trial, averaging a survival rate of 66.7% overall, owing largely to environmental factors rather than susceptibility to disease.
The American Elm cultivar Ulmus americana 'New Harmony' was raised by the Maryland Agricultural Research Service and released by the United States National Arboretum in 1995, along with 'Valley Forge'. 'New Harmony' proved the most successful U. americana cultivar in the US National Elm Trial, averaging a survival rate of 85.5% overall.
The Chinese Elm cultivar Ulmus parvifolia 'Burgundy' is a small American development.
Ulmus parvifolia 'Emer II' or 'Emerald Vase' is a Chinese Elm cultivar that was cloned from a tree planted circa 1910 on the University of Georgia campus at Athens.
The Chinese Elm cultivar Ulmus parvifolia 'Emer I' or 'Emerald Isle' was cloned from a tree planted circa 1920 on the University of Georgia campus at Athens.
The Chinese Elm cultivar Ulmus parvifolia 'Dynasty' is a United States National Arboretum introduction reputed to be very fast-growing.
The Chinese Elm cultivar Ulmus parvifolia 'King's Choice' is one of the early American selections best known for its winter hardiness, able to withstand temperatures of -30 deg. Celsius. 'King's Choice' was patented in 1985.
The Japanese elm cultivar Ulmus davidianavar.japonica 'Prospector' was originally treated as a cultivar of Wilson's elm U. wilsonianaSchneid., a species sunk as Ulmus davidiana var. japonica by Fu. A U.S. National Arboretum introduction, it was selected in 1975 from a batch of 1965 seedlings in Delaware, Ohio, and released without patent restrictions in 1990. 'Prospector' proved moderately successful in the US National Elm Trial, averaging a survival rate of 76% overall.
Ulmus 'Patriot' is a hybrid cultivar raised by the United States National Arboretum in 1980. Derived from a crossing of the American hybrid 'Urban' with the Wilson's Elm cultivar 'Prospector', 'Patriot' was released to commerce, free of patent restrictions, in 1993. Tested in the US National Elm Trial coordinated by Colorado State University, 'Patriot' averaged a survival rate of 85% after 10 years.