Elm Ave 2

Elms are deciduous and semi-deciduous trees comprising the flowering plant genus ''Ulmus'' in the plant family Ulmaceae. They are distributed over most of the Northern Hemisphere, inhabiting the temperate and tropical- montane regions of North America and Eurasia, presently ranging southward in the Middle East to Lebanon and Israel,Flora of Israel Online
Ulmus minor Mill. , Flora of Israel Online
accessdate: July 28, 2020 and across the Equator in the Far East into Indonesia.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, US.

Elms are components of many kinds of natural forests. Moreover, during the 19th and early 20th centuries, many species and cultivars were also planted as ornamental street, garden, and park trees in Europe, North America, and parts of the Southern Hemisphere, notably Australasia. Some individual elms reached great size and age. However, in recent decades, most mature elms of European or North American origin have died from Dutch elm disease, caused by a microfungus dispersed by bark beetles. In response, disease-resistant cultivars have been developed, capable of restoring the elm to forestry and landscaping.

Description

The genus is hermaphroditic, having apetalous perfect flowers which are wind-pollinated. Elm leaves are alternate, with simple, single- or, most commonly, doubly serrate margins, usually asymmetric at the base and acuminate at the apex. The fruit is a round wind-dispersed samara flushed with chlorophyll, facilitating photosynthesis before the leaves emerge.Heybroek, H. M., Goudzwaard, L, Kaljee, H. (2009). ''Iep of olm, karakterboom van de Lage Landen'' (:Elm, a tree with character of the Low Countries). KNNV, Uitgeverij. The samarae are very light, those of British elms numbering around 50,000 to the pound (454 g).Edlin, H. L. (1947). ''British Woodland Trees'',  p.26. 3rd. edition. London: B. T. Batsford Ltd. (Very rarely anomalous samarae occur with more than two wings.) All species are tolerant of a wide range of soils and pH levels but, with few exceptions, demand good drainage. The elm tree can grow to great height, often with a forked trunk creating a vase profile.

Image: Sapporo Autumn Gold, Florence.jpg, 'Sapporo Autumn Gold', Antella, Florence
Image:Ulmus glabra.jpg, Wych elm (''Ulmus glabra'') leaves and seeds
Image:Ulmus_rubra_leaf.jpg, Asymmetry of leaf, slippery elm ''U. rubra''
Image:Mature Ulmus rubra bark.jpg, Mature bark, slippery elm ''U. rubra''
Image:Columella flowers.jpg, Flowers of the hybrid elm cultivar 'Columella'
Image:Winged_Elm_Ulmus_alata_2009-05-10.jpg, Corky wings, winged elm ''U. alata''
Image:laciniata samara.jpg, ''U. laciniata'' samara
Image:Lovers' Elm, Gwynne estate, Dufferin Street.jpg, ''U. americana'', Dufferin St., Toronto, c. 1914
File:榔榆 Ulmus parvifolia 20210908101019 02.jpg, ''Ulmus parvifolia'' bark

Taxonomy

There are about 30 to 40 species of ''Ulmus'' (elm); the ambiguity in number results from difficulty in delineating species, owing to the ease of hybridization between them and the development of local seed-sterile vegetatively propagated microspecies in some areas, mainly in the Ulmus field elm ('' Ulmus minor'') group. Oliver Rackham Rackham, Oliver (1980). ''Ancient woodland: its history, vegetation and uses''. Edward Arnold, London describes ''Ulmus'' as the most critical genus in the entire British flora, adding that 'species and varieties are a distinction in the human mind rather than a measured degree of genetic variation'. Eight species are endemic to North America and three to Europe, but the greatest diversity is in Asia with approximately two dozen species. The oldest fossils of ''Ulmus'' are leaves dating Paleocene, found across the Northern Hemisphere.

The classification adopted in the List of elm species is largely based on that established by Brummitt.Brummitt, R. K. (1992). ''Vascular Plant Families & Genera''. Royal Botanic Garden, Kew, London, UK. A large number of synonyms have accumulated over the last three centuries; their currently accepted names can be found in the list of Elm synonyms and accepted names.

Botanists who study elms and argue over elm identification and classification are called "pteleologists", from the Greek πτελέα (elm).

As part of the suborder urticalean rosids, they are distantly related to cannabis, mulberries, figs, hops, and nettles.

Ecology

Propagation

Elm propagation methods vary according to elm type and location, and the plantsman's needs. Native species may be propagated by seed. In their natural setting, native species, such as wych elm and European white elm in central and northern Europe and field elm in southern Europe, set viable seed in "favourable" seasons. Optimal conditions occur after a late warm spring.Richens, R. H. (1983). ''Elm''. Cambridge University Press. After pollination, seeds of spring-flowering elms ripen and fall at the start of summer (June); they remain viable for only a few days. They are planted in sandy potting soil at a depth of 1 cm, and germinate in three weeks. Slow-germinating American elm will remain dormant until the second season.forestry.about.com/od/treeplanting/qt/seed_elm.htm Seeds from autumn-flowering elms ripen in the fall and germinate in the spring. Since elms may hybridize within and between species, seed propagation entails a hybridisation risk. In unfavourable seasons, elm seeds are usually sterile. Elms outside their natural range, such as English elm ''U. minor'' 'Atinia', and elms unable to pollinate because pollen sources are genetically identical, are sterile and are propagated by vegetative reproduction. Vegetative reproduction is also used to produce genetically identical elms (clones). Methods include the winter transplanting of root suckers; taking hardwood cuttings from vigorous one-year-old shoots in late winter, taking root cuttings in early spring; taking softwood cuttings in early summer; grafting; ground and air layering; and micropropagation. A bottom heat of 18 °C and humid conditions are maintained for hard- and softwood cuttings. The transplanting of root suckers remains the easiest most and commont propagation method for European field elm and its hybrids. For specimen urban elms, grafting to wych-elm rootstock may be used to eliminate suckering or to ensure stronger root growth. The mutant-elm cultivars are usually grafted, the "weeping" elms 'Camperdown' and 'Horizontalis' at , the dwarf cultivars 'Nana' and 'Jacqueline Hillier' at ground level. Since the Siberian elm is drought tolerant, in dry countries, new varieties of elm are often root-grafted onto this species.Clouston, B., Stansfield, K., eds., ''After the Elm'' (London, 1979)

Image:Ulmus minor MHNT.BOT.2010.12.3.jpg, Ripe samarae of field elm
Image:Rock Elm seedling.JPG, Rock elm ''Ulmus thomasii'' germinating
Image:Klijavac ulmus glabra goc 0427.jpg, Seedling of wych elm ''U. glabra''
Image:Ulmus minor 14.jpg, Root-suckers spreading from field elm ''U. minor''
Image:Root cuttings of Ulmus 'Dodoens'.jpg, Root cuttings of ''U.'' 'Dodoens'
Image:Elm clone rooted hardwood cutting Faculty of Forestry Belgrade 1983.09.01.jpg, Rooted hardwood elm cutting
Image:Rooting of softwood cuttings of elm under the mist propagation system.jpg, Rooting of softwood cuttings under mist
Image:Ulmus campestris 'ARGENTEOVARIEGATA'.jpg, Mutant variegated smooth-leafed elm graft
Image:Air layering of Ulmus pumila Faculty of Forestry Belgrade 7.6.1986.jpg, Air layering of ''U. pumila''
File:Ulmus chenmoui in vitro.jpg, In vitro propagation of ''U. chenmoui'' by bud meristem
File:Ulmus (unknown cultivar). Royal Terrace, Edinburgh (5).jpg, Aerial roots, hybrid elm cultivar

Associated organisms

File:20130702Ulme Saarbruecken1.jpg, Pouch leaf galls on a wych elm ( aphid ''Tetraneura ulmi''), Germany
File:Tetraneura ulmi (Aphididae sp.) gall, Elst (Gld), the Netherlands.jpg, Pouch leaf gall on elm leaf (aphid ''T. ulmi''), the Netherlands
File:Colopha compressa 1 beentree.jpg, Cockscomb leaf galls (aphid ''Colopha compressa''), Poland
File:Eriosoma lanuginosum 1.JPG, Bladder leaf galls on elm leaves (aphid ''Eriosoma lanuginosum''), Italy
File:Eriosoma lanuginosum 2.JPG, Bladder leaf galls on a narrow-leaved elm (aphid '' E. lanuginosum''), Italy
File:Colopha compressa 4 beentree.jpg, Aphids in leaf gall, Poland
File:Ulmus-minor---Eriophyes-ulmicola-agallas.jpg, Pimple leaf galls on a field elm (mite ''Eriophyes ulmi''), Spain
File:WLH Julita.JPG, White-letter hairstreak ''Satyrium w-album'', on , Sweden: The larvae feed only on elm.
File:Satyrium w-album egg1.jpg, Egg of ''Satyrium w-album'' near flower-bud of an elm
File:01a Scolytus multistriatus Imago 20fach rechte Seite.jpg, Elm-bark beetle ''Scolytus multistriatus'' (size: 2–3 mm), a vector for Dutch elm disease
File:04 Scolytus multistriatus Fraßbild.jpg, ''Scolytus multistriatus'' galleries under elm bark
File:Xanthogaleruca luteola 1.JPG, Elm-leaf beetle '' Xanthogaleruca luteola'', which causes serious damage to elm foliage
File:Xanthogaleruca luteola 20060905 525 part.jpg, ''Xanthogaleruca luteola'' caterpillar on elm leaf, Germany
File:Xanthogaleruca luteola 20060905 530.jpg, Elm-leaf damage caused by ''X. luteola'', Germany
File:Slime flux on Camperdown elm.png, Bacterial infection ''Erwinia carotovora'' of elm sap, which causes slime flux (wetwood) and staining of the trunk (here on a 'Camperdown' elm)

Pests and diseases

Dutch elm disease

Dutch elm disease (DED) devastated elms throughout Europe and much of North America in the second half of the 20th century. It derives its name "Dutch" from the first description of the disease and its cause in the 1920s by Dutch botanists Bea Schwarz and Christina Johanna Buisman. Owing to its geographical isolation and effective quarantine enforcement, Australia has so far remained unaffected by DED, as have the provinces of Alberta and British Columbia in western Canada.

DED is caused by a microfungus transmitted by two species of '' Scolytus'' elm-bark beetles, which act as vectors. The disease affects all species of elms native to North America and Europe, but many Asiatic species have evolved antifungal genes and are resistant. Fungal spores, introduced into wounds in the tree caused by the beetles, invade the xylem or vascular system. The tree responds by producing tyloses, 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 with the fungus of over 300 clones of the European species failed to find a single variety that possessed of any significant resistance.

The first, less aggressive strain of the disease fungus, ''Ophiostoma ulmi'', arrived in Europe from Asia in 1910, and was accidentally introduced to North America in 1928. It was steadily weakened by viruses in Europe and had all but disappeared by the 1940s. However, the disease had a much greater and longer-lasting impact in North America, owing to the greater susceptibility of the American elm, ''Ulmus americana'', which masked the emergence of the second, far more virulent strain of the disease ''Ophiostoma novo-ulmi''. It appeared in the United States sometime in the 1940s, and was originally believed to be a mutation of ''O. ulmi''. Limited gene flow from ''O. ulmi'' to ''O. novo-ulmi'' was probably responsible for the creation of the North American subspecies ''O. novo-ulmi'' subsp. ''americana''. It was first recognized in Britain in the early 1970s, believed to have been introduced via a cargo of Canadian rock elm destined for the boatbuilding industry, and rapidly eradicated most of the mature elms from western Europe. A second subspecies, ''O. novo-ulmi'' subsp. ''novo-ulmi'', caused similar devastation in Eastern Europe and Central This subspecies, which was introduced to North America, and like ''O. ulmi'', is thought to have originated in Asia. The two subspecies have now hybridized in Europe where their ranges have overlapped.Webber, J. (2019). What have we learned from 100 years of Dutch Elm Disease? ''Quarterly Journal of Forestry''. October 2019, Vol. 113, No.4,  p.264-268. Royal Forestry Society, UK. The hypothesis that ''O. novo-ulmi'' arose from a hybrid of the original ''O. ulmi'' and another strain endemic to the Himalayas, ''Ophiostoma himal-ulmi'', is now discredited.Brasier, C. M. & Mehotra, M. D. (1995). Ophiostoma himal-ulmi sp. nov., a new species of Dutch elm disease fungus endemic to the Himalayas. ''Mycological Research'' 1995, vol. 99 (2), 205–215 (44 ref.) . Elsevier, Oxford, UK.

No sign indicates the current pandemic is waning, and no evidence has been found of a susceptibility of the fungus to a disease of its own caused by d-factors: naturally occurring virus-like agents that severely debilitated the original ''O. ulmi'' and reduced its sporulation.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.

Elm phloem necrosis

Elm phloem necrosis (elm yellows) is a disease of elm trees that is spread by leafhoppers or by root grafts.Elm Yellows
". Elmcare.Com. 19 March 2008. This very aggressive disease, with no known cure, occurs in the Eastern United States, southern Ontario in Canada, and Europe. It is caused by phytoplasmas that infect the phloem (inner bark) of the tree.Price, Terry.
Wilt Diseases
". Forestpests.Org. 23 March 2005. 19 March 2008. Infection and death of the