Ulmus'Nanguen' is a complex fourth generation Dutch hybridcultivar raised at the Dorschkamp Research Institute for Forestry & Landscape Planning, Wageningen. was derived from the cross 'Plantyn' ×, an ancestry comprising four field elms, a wych elm, the curious Exeter Elm, and a frost-resistant selection of the Himalayan elm. Originally identified as clone 812, was not promoted by the Dutch owing to unfounded fears that it may prove susceptible to coral spot fungus. Instead, 812 was acquired by the French Institut National de la Recherche Agronomique, which subjected the tree to 20 years of field trials in the Bois de Vincennes, Paris, before patenting and release in 2002 as 'Nanguen' =. has been deemed the modern cultivar most closely resembling the native European elms.
Description
The stem of typically forks at a height of 1-2 m, where 3-5 steeply ascending branches develop in conjunction with more obtusely angled lower side branches to form an amorphous open crown. The ultimate size and shape of this cultivar remain unknown but, given its ancestry, it should make a large tree. The trees planted in the Bois de Vincennes attained an average height of 12.5 m with a trunk diameter of 22 cm at 20 years of age. Quick growing on moist, well-drained soils, increasing in height by an average of 80 cm per annum, the tree commences flowering in late March when aged seven years. The leaves are elliptic to orbicular < 11 cm long × 9 cm wide, the acuminate apex far less pronounced than in most other elms, with coarse, doubly serrate margins; the upper surface is rough. The leaves flush relatively late, rarely before mid-May in England. The samarae are obovate, slightly notched at the outer end, 14-22 mm long by 11-17 mm broad. The seed is not central but slightly nearer the notch, and ripens in late May.
Pests and diseases
exhibited a high resistance to Dutch elm disease when inoculated with unnaturally high doses of the causal fungus Ophiostoma novo-ulmi, and was rated 5 out of 5 in Dutch tests. Tests in France by INRA confirmed the tree has 'highly resistant'. In trials conducted by the Istituto per la Protezione delle Piante, Florence, suffered 19.8% defoliation and 11.7% dieback when inoculated, compared with 2.8% and 1.2% resp. for 'Sapporo Autumn Gold', and 50% and 35.5% resp. for 'Lobel'. The presence of U. wallichiana in the ancestry of poses the risk of susceptibility to elm yellows, which seriously damaged its Dutch stablemate 'Lobel' used as a control in the Italian elm breeding programme.
Cultivation
The cultivar is now being widely planted in cities, notably Paris, and rural areas of France. In trials in southern England, the tree has proven very hardy, tolerant of sea winds, summer droughts, and ground waterlogged during winter. However, top-growth can often outpace root development, leaving some trees susceptible to wind-rock when young and necessitating staking for up to six years. is cold hardy, and has survived winter temperatures as low as - 30° C in Sweden. was introduced to the UK by the Hampshire & Isle of Wight Branch, Butterfly Conservation, in 2001, as part of its assessment of DED-resistant cultivars as potential hosts of the endangered White-letter Hairstreak. The plants were donated by SAPHO ahead of its release to commerce. was introduced to North America in 2010, with the supply of two small specimens to the USDA, Washington, D.C., released from quarantine in 2013. is not known to have been introduced to Australasia. Increasing by softwood cuttings is relatively straightforward, however these lose their viability as the trees mature, and French nurseries now resort to grafting onto 'Sapporo Autumn Gold' rootstocks. As the latter does not sucker from roots, the practice eliminates natural vegetative regeneration
Hybridization
has been found to hybridize readily with Ulmus minor in trials by IRSTEA in France, often producing copious quantities of fertile seed.
Conservation role
Over 5000 were planted on the Isle of Wight by , and in smaller numbers in Hampshire by Butterfly Conservation and the Forestry Commission, in the hope the tree would host the white-letter hairstreak butterfly, a monophagic species which remains in serious decline as a consequence of Dutch elm disease. This was confirmed in 2015 with the discovery of the butterfly breeding on specimens planted in 2003 at Towngate, Newport, Isle of Wight.
Etymology
The selling name is the French derivation of Lutetia, the ancient Roman name for the settlement which later became Paris. The name was adopted in recognition of the trials of the cultivar conducted by INRA in the Bois de Vincennes.
Accessions
Europe
Brighton & Hove City Council, UK. NCCPG Elm Collection. Stanmer Nursery.
Great Fontley Farm, Fareham, UK. Butterfly Conservation Elm Trials plantation, Home Field and the Platt, five small whips donated by SAPHO in 2002.
Longstock Park Arboretum, UK. One juvenile specimen planted 2010.
