Elm

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For other uses, see Elm (disambiguation).

{{Taxobox | color = lightgreen | name = Elm | image = Mature Ulmus rubra in graveyard.jpg | image_width = 240px | image_caption = Mature Slippery Elm | regnum = Plantae | divisio = Magnoliophyta | classis = Magnoliopsida | ordo = Rosales | familia = Ulmaceae | genus = Ulmus | genus_authority = L. | subdivision_ranks = Species | subdivision = See text. }}

Elms are deciduous trees of the genus Ulmus, family Ulmaceae, native to temperate regions of the Northern Hemisphere. They have alternate, simple, single- or doubly-serrate leaves, usually with asymmetric bases, often rough with fine bristles. The fruit is a round samara.

There are between 20 to 45 species of elm; the ambiguity in the number is a result of difficult species delimitations in elms, owing to the ease of hybridization between them and the development of local seed-sterile vegetatively-propagated microspecies in some areas, mainly in the field elm group.

Classification
  • "Mountain elms": spring flowering; flowers subsessile; leaves very rough above.
    • Ulmus bergmanniana. Eastern Asia. <26m tall, with large leaves up to 16cm long and 8cm wide. Very closely related to U. glabra.
    • Ulmus castaneifolia. China. <20m tall, with slender stem <50cm in diameter and thick, corky bark. Leaves <15cm long, 6cm wide, densely hirsute when young.
    • Ulmus changii. China. <20m tall, with smooth, glabrous, ovate leaves up to 11cm long.
    • Ulmus elongata. China. <30m tall, stem <80cm in diameter with exfoliating bark. Long, elliptic leaves <19cm and distinctive shuttle-shaped samaras.
    • Ulmus gaussennii. China. <25m tall, with black to very dark grey scabrous bark. Leaves <11cm long, densely pubescent when young.
    • Ulmus glabra - Wych Elm. Europe, Asia. Popular cultivars include 'Camperdownii', 'Exoniensis' [Exeter Elm], 'Horizontalis', 'Nana'.
    • Ulmus glaucescens. Northern China. <18m tall, with exfoliating, mottled bark. Small, usually ovate leaves <5cm long. Exceptional resistance to drought, but intolerant of wet soils.
    • Ulmus laciniata - Manchurian Elm. Eastern Asia. <27m tall and slender stem <50cm in diameter. Distinctive laciniate, often obtriangular leaves <18cm long, with up to seven apical lobes. Closely related to U. glabra, it only grows well in sheltered, humid valleys.
    • Ulmus lamellosa. China. <12m tall, with rounded crown and slender trunk with mottled, flaking bark. Good resistance to Dutch elm disease and leaf beetles, but intolerant of wet soils.
    • Ulmus macrocarpa. Northeastern Asia. <12m tall, with thick, leathery obovate leaves <9cm long. Very large sub-orbicular samaras <47mm long and <39mm wide. Demands well-drained soil. Good resistance to Dutch elm disease.
    • Ulmus microcarpa. China (Xizang {:Tibet} only). <30m tall, with stem <80cm in diameter. Large, glabrous leaves <17cm long, but very small samaras <8mm in diameter.
    • Ulmus prunifolia. China. <30m tall, slender stem <45cm in diameter with smooth dark grey bark. Narrow, glabrescent leaves <11 cm long.
    • Ulmus rubra - Slippery Elm or Red Elm. Eastern North America.
    • Ulmus uyematsui. Arishan Elm. Taiwan. <25m tall with dark grey bark exfoliating in irregular flakes. Leaves elliptic, < 11cm long. [1]
    • Ulmus wallichiana - Himalayan Elm or Kashmir Elm. Northern Afghanistan, northern Pakistan, western Himalaya.
  • "Field elms": spring flowering; flowers subsessile; leaves usually smooth above.
    • Ulmus chenmoui. China. <20m tall, with exfoliating bark and broad, obovate leaves <18cm long.
    • Ulmus chumlia. Himalaya. <25m tall, with spreading crown and sinuous branches. Leaves narrowly obovate, <10cm long and <4cm wide.
    • Ulmus davidiana - North-east Asia, inc. Japan. <15m tall, leaves obovate <10cm long by 5.5cm broad. Two varieties recognized by Fu:
      • Ulmus davidiana var. davidiana - David Elm. China. <12m tall, vase-shaped. Intolerant of exposed conditions and wet soils.
      • Ulmus davidiana var. japonica - Japanese Elm. North-east Asia, inc. Japan. 'Discovery', 'Freedom', 'Jacan', 'Mitsui Centennial', and 'Thomson' are hardy varieties selected for planting in Canada in the 1980s.
    • Ulmus harbinensis. China (Heilongjiang only). <15m tall; leaves <5.5cm long and <3.5cm broad.
    • Ulmus lanceaefolia. Western China (Yunnan only), India (Darjeeling area), Bhutan, Sikkim, Bangladesh, Laos, Myanmar. A very large tree, <45m tall, with spreading crown. The bark of the trunk exfoliates in small scales. Oblong to elliptic leaves, <8cm long and <2.5cm wide. Evergreen in the southern part of its range.
    • Ulmus minor - Field Elm. Europe, Asia Minor, Algeria. An extremely variable species, its taxonomy remains a matter of much contention. Four British subspecies or varieties, and several cultivars, identified by Richens, all very susceptible to Dutch elm disease.
      • Ulmus minor subsp. angustifolia. syns. U. minor var. cornubiensis, U. stricta. - Cornish Elm. England, France; local endemic. Narrow tree <25m tall, with a crown of short ascending branches. Slow growing, and once valued for its very tough timber.
      • Ulmus minor subsp. minor, syn. U. carpinifolia - Smooth-leaved Elm or Narrow-leaved Elm. Europe, Turkey, Iran, Israel, Algeria. Disease-resistant cultivars: 'Christine Buisman', released 1936, and 'Bea Schwarz' 1948.
      • Ulmus minor var. plotii, syn. var. lockii - Plot's Elm, Goodyer's Elm or Lock Elm. England; local endemic. Small tree with stem curving at its peak with pendent branches to form a narrow crown cocked to one side.
      • Ulmus minor var. vulgaris, syn. U. procera - English Elm or Atinian Elm. England, Italy, Spain.
      • Ulmus minor 'Sarniensis' - Jersey Elm, also Guernsey Elm, Wheatley Elm, Southampton Elm. Channel Islands, France; local endemic, widely cultivated in Britain. Pyramidal tree <25m tall with straight, ascending branches and pointed crown. Golden form once very popular, sometimes known as Dickson Elm.
    • Ulmus pseudopropinqua. Northern China (Inner Mongolia). <10m tall with corky branches. Good resistance to Dutch elm disease and elm beetles.
    • Ulmus pumila - Siberian Elm. China, India (Kashmir), Siberia. American cultivars include 'Dropmore', 'Park Royal', 'Lincoln' and 'Chinkota'.
    • Ulmus szechuanica. China. <18m tall, with umbrella-like canopy. Leaves obovate, glabrescent, <9cm long, dark red on emergence, and again in autumn.
    • Ulmus villosa - Cherry Bark Elm. India (Kashmir). <25m tall, with broad crown <14m wide and pendulous branches. Leaves oblong-elliptic acute <11cm long and <4cm broad. A long-lived species, sacred specimens planted around temples are over 800 years old. Sometimes misidentified as U. wallichiana (see link). [2]
    • Ulmus wilsoniana - Wilson's Elm. Western China. Now treated as conspecific with U. davidiana by Fu. 'Prospector' is a U. S. National Arboretum selection, vase-shaped and growing to 12m tall, with deep-green glabrous leaves resistant to elm leaf beetle.
  • "White elms": spring flowering; flowers pedunculate
    • Ulmus alata - Winged Elm. Eastern North America.
    • Ulmus americana - American Elm. North America east of the Rockies. Cultivars with resistance to Dutch elm disease include: 'American Liberty', 'Brandon', 'Delaware', 'Independence', 'Jefferson', 'New Harmony', 'Princeton', 'Valley Forge' and 'Washington'.
    • Ulmus androssowii - Narwan Elm. China (Yunnan, Sichuan, and Xijang {Tibet}). <20m tall, with ovate or elliptic glabrous leaves <8cm long and <2.5cm wide.
    • Ulmus laevis - European White Elm or Fluttering Elm, Spreading Elm, (USA only) Russian Elm. Eastern Europe, Western Asia.
    • Ulmus thomasii - Rock Elm. Eastern North America.
  • "Autumn-flowering elms": autumn flowering.
    • Ulmus crassifolia - Cedar Elm. Eastern North America.
    • Ulmus parvifolia - Chinese Elm or Lacebark Elm. China. 27 known American cultivars including: 'A. Ross Central Park' (Central Park Splendor™), 'Bosque', 'Drake', 'Dynasty', 'Emer I' (Athena™), 'Emer II' (Allee™), 'King's Choice', 'Ohio', 'Pathfinder', 'Sempervirens'. Many others such as 'Hokkaido' are miniatures raised for bonsai.
    • Ulmus serotina - September Elm. Eastern North America.
    • Ulmus tonkinensis. Western China, Northern Vietnam. Evergreen tree with exfoliating bark. Ovate-lanceolate glabrous leaves <10cm long and <3cm wide.
  • Hybrids and hybrid origin cultivars.
    • Ulmus × brandisiana. U. chumlia × U. wallichiana. Naturally-occurring hybrid in Pakistan and north-west India.
    • Ulmus × elegantissima 'Jacqueline Hillier'. English hybrid of uncertain parentage, possibly U. glabra × U. minor var. plotii.
    • Ulmus × hollandica - 'Dutch Elm'. U. glabra × U. minor. Naturally occurring hybrid found across much of Europe.
    • Ulmus 'Cathedral'. U. pumila × U. davidiana var. japonica. American hybrid, more closely resembling its male parent, U. davidiana var. japonica than its siblings 'New Horizon' and 'Sapporo Autumn Gold' but not as resistant to Dutch elm disease.
    • Ulmus 'Charisma'. ((U. davidiana var. japonica × U. wilsoniana) × (U. davidiana var. japonica × U. pumila)). American hybrid.
    • Ulmus 'Clusius'. (U. glabra Exoniensis × U. wallichiana) × U. × hollandica 'Bea Schwarz'. Dutch hybrid released 1983. Similar to 'Lobel', but with slightly improved resistance to Dutch elm disease.
    • Ulmus 'Columella'. 'Plantyn' or 'Plantijn' selfed. Dutch hybrid released 1989.
    • Ulmus 'Commelin'. U. × hollandica 'Vegeta' × U. minor. Dutch hybrid released 1960. Fast growing, but only moderate resistance to disease and wind damage.
    • Ulmus 'Coolshade'. U. rubra × U. pumila. American hybrid.
    • Ulmus 'Dodoens'. U. glabra × U. wallichiana selfed. Dutch hybrid released 1973. Strong, fast growing, but only moderately resistant to Dutch elm disease.
    • Ulmus 'Frontier'. U. minor × U. parvifolia. <13m tall, with glabrous leaves turning dark red in autumn. Good tolerance of arid conditions.
    • Ulmus 'Green King'. U. rubra × U. pumila. American hybrid.
    • Ulmus 'Groeneveld'. U. minor × U. glabra. Dutch hybrid released 1960. Slower growing than 'Commelin', and only moderately resistant to disease. Planted mostly in Dutch towns.
    • Ulmus 'Homestead'. U. pumila × ((U. hollandica 'Vegeta' × U. minor) × (U. pumila × U. minor)). U. S. National Arboretum hybrid. Fast growing, producing a pyramidal crown, and well-suited to city conditions. High resistance to Dutch elm disease, but unsuited to arid conditions.
    • Ulmus 'Lobel'. (U. glabra Exoniensis × U. wallichiana) × U. × hollandica 'Bea Schwarz'. Dutch hybrid released 1973. Fastigiate, small-crowned, small-leaved tree resistant to sea winds, but only moderately resistant to Dutch elm disease.
    • Ulmus 'Morton' (Accolade ™). U. davidiana var. japonica × U. wilsoniana. American hybrid >30m tall, vase-shaped tree with small, glossy, dark-green leaves. Highly resistant to Dutch elm disease, but not available in Europe.
    • Ulmus 'Morton Glossy' (Triumph ™). 'Morton' × 'Vanguard'. <20m tall, with upright oval- to vase-shape, and dark green glabrous leaves.
    • Ulmus 'Morton Plainsman' (Vanguard ™). U. pumila × U. japonica. American hybrid <15m tall, with rounded crown. Drought resistant.
    • Ulmus 'Morton Red Tip' (Danada Charm ™). U. davidiana var. japonica × U. wilsoniana. <25m tall, vase-shaped with arching limbs, and dark green leaves. A seedling of (Accolade ™).
    • Ulmus 'Morton Stalwart' (Commendation ™). (U. davidiana var. japonica × U. wilsoniana) × (U. pumila × U. minor). <20m tall, with upright, oval shape.
    • Ulmus 'Nanguen' (Lutèce ™). 'Plantyn' × (U. × hollandica 'Bea Schwarz' × U. × hollandica 'Bea Schwarz' selfed). Dutch hybrid, released 2002. [3].
    • Ulmus 'New Horizon'. U. pumila × U. davidiana var. japonica . American hybrid patented 1995.
    • Ulmus 'Patriot'. 'Urban' × U. wilsoniana 'Prospector'. American hybrid with vase-shaped crown. High resistance to Dutch elm disease and elm yellows. Very fast growing, capable of exceeding 1m per annum.
    • Ulmus 'Pioneer'. U. glabra × U. minor. U. S. National Arboretum hybrid. Dense, spherical crown. Only moderately resistant to Dutch elm disease.
    • Ulmus 'Plantyn' or 'Plantijn'. (U. glabra Exoniensis × U. wallichiana) × (U. minor × U. minor). Dutch hybrid released 1973. Fast growing with broad crown. Tolerant of sea winds, but only moderately resistant to Dutch elm disease.
    • Ulmus 'Plinio'. 'Plantyn' × U. pumila. Italian hybrid released 2003.
    • Ulmus 'Regal'. U. pumila × ((U. hollandica 'Vegeta' × U. minor) × (U. pumila × U. minor)). American hybrid with upright columnar form making it suitable for urban planting. High resistance to Dutch elm disease, and tolerant of arid conditions.
    • Ulmus 'San Zanobi'. 'Plantyn' × U. pumila. Italian hybrid released 2003.
    • Ulmus 'Sapporo Autumn Gold'. U. pumila × U. davidiana var. japonica. From a chance crossing in Sapporo, Japan. Grows quickly to form vase-shaped crown, although young trees need pruning to produce clean stem. Highly resistant to Dutch elm disease, and now also widely available in Europe.
    • Ulmus 'Urban'. (U. × hollandica 'Vegeta' × U. minor) × U. pumila. U. S. National Arboretum hybrid.
    • Ulmus 'Vegeta' - Huntingdon Elm, syn. Chichester Elm. U. glabra × U. minor selfed. Old English cultivar raised circa 1750.
    • Ulmus 'Wredei' - Golden Elm. U. × hollandica cultivar.
    • and many more without formal hybrid names

The other genera in the Ulmaceae are Zelkova (Zelkova) and Planera (Water-elm). Celtis (Hackberry or Nettle Tree), formerly included in Ulmaceae, is now treated in the family Cannabaceae.

Image:Ulmus glabra1.jpg Image:Wych elm flower.jpg

Contents

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Cultivation and uses

Elm wood is valued for its interlocking grain, and consequent resistance to splitting, with significant uses in chair seats and coffins. The wood is also resistant to decay when permanently wet, and was used for making water pipes during the mediaeval period in Europe. Elms also have a long history of cultivation for fodder, with the leafy branches cut for livestock. The bark, cut into strips and boiled, sustained much of the rural population of Norway during the famine in the mid-19th century.

From the 18th century to the early 20th century, elms were among the most widely planted ornamental tree in both Europe and North America. They were particularly popular as a street tree in avenue plantings in towns and cities, creating high tunneled effects.

In Europe, the Wych Elm U. glabra and the Smooth-leaved Elm U. minor were the most widely planted, with the former in northern areas (Scandinavia, northern Britain), and the latter further south. The hybrid between these two, Dutch Elm U. × hollandica, occurred naturally and was also commonly planted.

In North America the main species used was the American Elm U. americana, which has unique properties that made it ideal for such use; rapid growth, wide adaptation to a broad range of climates and soils, strong wood, resistant to wind damage, and vase-like growth habit requiring minimal pruning.

From about 1850 to 1920 the most prized small specimen elm was the Camperdown Elm, a contorted weeping cultivar of the Wych Elm Ulmus glabra 'Camperdown', grafted on a standard Wych Elm trunk to give a wide, spreading and weeping fountain shape in large garden spaces.

Large numbers of English Elms U. minor var. vulgaris were planted in Australia in the early 20th century, although the tree is not native to the island-continent.

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Dutch Elm Disease

Dutch elm disease has devastated elms throughout Europe and North America. It is caused by the micro- fungus Ophiostoma novo-ulmi transmitted by two species of Scolytus elm-bark beetle which act as vectors. The disease affects all species of elm native to North America and Europe, but many Asiatic species have anti-fungal genes and are resistant. Fungal spores, introduced into wounds in the tree caused by the beetles, germinate in the vascular system, effectively blocking the flow from roots to leaves. Woodland trees in North America are not quite as susceptible to the disease because they usually lack the root-grafting of the urban elms and are somewhat more isolated from each other. In France, inoculation of over three hundred clones of the three European species with the fungus failed to find a single variety possessed of any significant resistance.

An earlier, less aggressive strain of the disease fungus, Ophiostoma ulmi, first appeared in Europe in 1910 and North America in 1928, but had declined by the 1940s. The second, far more virulent strain of the disease was identified in Europe in the late 1960s, and within a decade had killed over 20 million trees (approximately 75%) in the UK alone. The origin of the new strain remains a mystery; earlier believed to have been endemic to China, surveys there in 1986 found no trace of it, although bark beetles were common. The most popular hypothesis is that it arose from a hybrid between the original O. ulmi and another strain endemic to the Himalaya, O. himal-ulmi. While there is no sign of the current pandemic waning, there is some hope in the susceptibility of the fungus to a disease of its own caused by d-factors : naturally occurring virus-like agents that can severely debilitate it and reduce its sporulation.

Owing to its geographical isolation and effective quarantine enforcement, Australia has so far been unaffected by Dutch Elm Disease, and as such retains some of the world's best stands of English Elms; the long avenues of Royal Parade and St Kilda Road in Melbourne are perhaps the most beautiful examples [4].

The provinces of Alberta and British Columbia in western Canada are also free of Dutch Elm disease, although in 1998, one tree in southeastern Alberta was found diseased and thus had to be destroyed immediately before the disease could spread any further. Aggressive means are being taken to prevent any occurrences of the disease in these two provinces. In fact, Alberta has the world's largest stands of elms unaffected by the disease, and many streets and parks in Edmonton and Calgary are still lined with large numbers of healthy mature trees.

Resistant Trees

Efforts to develop resistant trees began in the Netherlands in 1928. Research was later conducted in north America, and continues to this day in Italy. Research has followed two paths.

Hybridization between Asiatic species and European elms, or between Asiatic elms alone, has now, after a number of false dawns, produced some fine trees. Hybrids with immunity or very high resistance to disease are now commercially available after over 20 years of field trials; several originated in the USA, two in the Netherlands, and two in Italy. However, some of these trees, notably those with the Siberian Elm U. pumila in their ancestry, will probably have a comparatively small mature size and lack the forms for which the iconic American and English Elms were prized. Several of the same have also proven unsuited to the oceanic climate conditions in northwestern Europe, notably because of their intolerance of ponding on poorly-drained soils in winter. Dutch hybridizations included the Himalayan Elm U. wallichiana as a source of anti-fungal genes and have proved more tolerant of waterlogged ground; they should also ultimately reach a greater size.

Separately, efforts have been made in the USA to develop resistant cultivars of American Elm. The 'Liberty Elm', available commercially, represents the results of one such effort, and though marketed as a single product, consists of five cultivars chosen at random. These cultivars were the result of field selection of trees that survived in a region where the disease was endemic, followed by 2-3 generations of selection. Some of the cultivars are patented. The 'Valley Forge' and 'New Harmony' elms are similar cultivars, produced using selection techniques similar to those used for the 'Liberty Elm'.

Since elms take decades to grow to maturity, and these introductions are recent, the performance and ultimate size of these trees in the countryside is not known with certainty.

A related effort is the commercial reintroduction of the 'Princeton Elm', which is a cultivar selected in 1920 for its landscape qualities. Large plantings have survived the disease, and testing in laboratory conditions revealed that this cultivar has considerable resistance. It was selected in 2006 by HRH The Prince of Wales to create an avenue from his residence Highgrove House to the Golden Bird statue on the boundary of his garden. It has also been chosen to replace elms killed by disease along Pennsylvania Avenue in front of the White House.

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Insect use

Many species of Lepidopteran larvae uses elm as a food plant; see list of Lepidoptera which feed on Elms. In Australia, introduced elm trees are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus. These burrow horizontally into the trunk then vertically down.

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References

  • Armstrong, J. V. & Sell, P. D. (1996). A revision of the British elms (Ulmus L., Ulmaceae): the historical background. Bot. J. Linn. Soc. 120: 39-50.
  • Brasier, C. M. (1996). New horizons in Dutch elm disease control. Pages 20-28 in: Report on Forest Research 1996. Forestry Commission. HMSO, London, UK.
  • Brookes A.H. (2006). An evaluation of disease-resistant hybrid and exotic elms as larval host plants for the White-letter Hairstreak butterfly Satyrium w-album, Part 1. Butterfly Conservation, Lulworth, UK.
  • Burdekin, D. A. & Rushforth, K. D. (Revised by Webber J. F. 1996). Elms resistant to Dutch elm disease. Arboricultural Research Note 2/96. Arboricultural Advisory and Information Service, Alice Holt, Farnham, UK.
  • Collin, E. (2001). Elm. In Teissier du Cros (Ed.) (2001) Forest Genetic Resources Management and Conservation. France as a case study. Ministry of Agriculture and Fisheries, Bureau of Genetic Resources. INRA DIC. France.
  • Cornell University: Elm hybrids (pdf file)
  • Elwes, H. J. & Henry, A. (1913). The Trees of Great Britain & Ireland. Vol. VII. pp 1848-1929. Private publication, Edinburgh. [5]
  • Fu, L., Xin, Y. & Whittemore, A. (2002). Ulmaceae, in Wu, Z. & Raven, P. (eds) Flora of China, Vol. 5 (Ulmaceae through Basellaceae). Science Press, Beijing, and Missouri Botanical Garden Press, St. Louis, USA. [6]
  • Melville, R. & Heybroek, H. (1971). Elms of the Himalaya. Kew Bulletin, Vol. 26 (1). Kew, London.
  • Northern Arizona University: Elm trials.
  • Richens, R. H. (1983). Elm. Cambridge University Press.
  • Santamour, J., Frank, S. & Bentz, S. (1995). Updated checklist of elm (Ulmus) cultivars for use in North America. Journal of Arboriculture, 21:3 (May 1995), 121-131. International Society of Arboriculture, Champaign, Illinois, USA.
  • Santini, A., Fagnani, A., Ferrini, F. & Mittempergher, L. (2002). 'San Zanobi' & 'Plinio' Elm Trees. HortScience, Vol. 37 (7) : 1139-1141. Dec. 2002.
  • Ware, G. (1995). Little-known elms from China: landscape tree possibilities. Journal of Arboriculture, (Nov. 1995). International Society of Arboriculture, Champaign, Illinois, USA.ast:Llamera

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