Elm

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Elm
Narrow-leafed Elm Ulmus minor subsp minor

East Coker, Somerset, UK.

Scientific classification
Kingdom:Plantae
(unranked):Angiosperms
(unranked):Eudicots
(unranked):Rosids
Order:Rosales
Family:Ulmaceae
Genus:Ulmus
L.
Species

See

 
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Elm
Narrow-leafed Elm Ulmus minor subsp minor

East Coker, Somerset, UK.

Scientific classification
Kingdom:Plantae
(unranked):Angiosperms
(unranked):Eudicots
(unranked):Rosids
Order:Rosales
Family:Ulmaceae
Genus:Ulmus
L.
Species

See

Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the plant family Ulmaceae. The genus first appeared in the Miocene geological period about 20 million years ago, originating in what is now central Asia.[1] These trees flourished and spread over most of the Northern Hemisphere, inhabiting the temperate and tropical-montane regions of North America and Eurasia, ranging southward across the Equator into Indonesia.

Elms are components of many kinds of natural forests; 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.

Elm leaves are alternate, with simple, single- or, most commonly, doubly serrate margins, usually asymmetric at the base and acuminate at the apex. The genus is hermaphroditic, having apetalous perfect flowers which are mostly wind-pollinated, although bees do visit them. The fruit is a round wind-dispersed samara flushed with chlorophyll, facilitating photosynthesis before the leaves emerge.[2] All species are tolerant of a wide range of soils and pH levels but, with few exceptions, demand good drainage.

The other genera of the Ulmaceae are Planera (water elm) and Zelkova (zelkova). The genus Celtis (hackberry or nettle tree), formerly included in the Ulmaceae, is now included in the family Cannabaceae.

Taxonomy[edit]

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 field elm (Ulmus minor) group. Rackham[3] describes Ulmus as the most difficult 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 a smaller number to Europe;[4] the greatest diversity is found in Asia.[5]

The classification adopted in the List of elm species, varieties, cultivars and hybrids is largely based on that established by Brummitt.[6] A large number of synonyms have accumulated over the last three centuries; their currently accepted names can be found in the list List of elm Synonyms and Accepted Names.

Etymology[edit]

The name Ulmus is the classical name for these trees, with the English name "elm" and many other European names derived from it.[7]

Ulmus americana, Dufferin St., Toronto, c.1914

Familiar species[edit]

The more abundant or better-known species of Ulmus include:

Pests and diseases[edit]

Dutch elm disease[edit]

Dutch elm disease (DED) devastated elms throughout Europe and much of North America in the second half of the 20th century. Owing to its geographical isolation and effective quarantine enforcement, Australia has so far remained unaffected by Dutch Elm Disease, as have the provinces of Alberta and British Columbia in western Canada.

DED is caused by a micro-fungus 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 evolved anti-fungal 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 three hundred clones of the European species failed to find a single variety possessed of any significant resistance.

The first, less aggressive strain of the disease fungus, Ophiostoma ulmi, arrived in Europe from the Far East in 1910, and was accidentally introduced to North America in 1928, but was steadily weakened by viruses and had all but disappeared in Europe by the 1940s. The second, far more virulent strain of the disease Ophiostoma novo-ulmi was identified in Europe in the late 1960s, and within a decade had killed over 20 million trees (approximately 75%) in the UK alone. Approximately three times more deadly, the origin of the new strain is again most likely the Far East; the hypothesis that it arose from a hybrid between the original O. ulmi and another strain endemic to the Himalaya, Ophiostoma himal-ulmi now discredited.[8]

There is no sign of the current pandemic waning, and no evidence 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.[9]

Elm phloem necrosis[edit]

Elm phloem necrosis (elm yellows) is a disease of elm trees that is spread by leafhoppers or by root grafts.[10] This very aggressive disease, with no known cure, occurs in the Eastern United States and southern Ontario in Canada. It is caused by phytoplasmas which infect the phloem (inner bark) of the tree.[11] Infection and death of the phloem effectively girdles the tree and stops the flow of water and nutrients. The disease affects both wild-growing and cultivated trees. Occasionally, cutting the infected tree before the disease completely establishes itself and cleanup and prompt disposal of infected matter has resulted in the plant's survival via stump-sprouts.

Insects[edit]

Most serious of the elm pests is the elm leaf beetle Xanthogaleruca luteola, which can decimate foliage, although rarely with fatal results. The beetle was accidentally introduced to North America from Europe. Another unwelcome immigrant to North America is the Japanese beetle Popillia japonica. In both instances the beetles cause far more damage in North America owing to the absence of the predators present in their native lands. In Australia, introduced elm trees are sometimes used as foodplants by the larvae of hepialid moths of the genus Aenetus. These burrow horizontally into the trunk then vertically down.[12][13]

Birds[edit]

Sapsucker woodpeckers have a great love of young elm trees.

Development of trees resistant to Dutch elm disease[edit]

Efforts to develop resistant cultivars began in the Netherlands in 1928 and continued, uninterrupted by World War II, until 1992.[14] Similar programmes were initiated in North America (1937), Italy (1978), and Spain (1990s). Research has followed two paths:

Species and species cultivars[edit]

In North America, careful selection has produced a number of trees resistant not only to disease, but also to the droughts and extremely cold winters afflicting the continent. Research in the USA has concentrated on the American Elm U. americana, resulting in the release of highly resistant clones, notably the cultivars 'Valley Forge' and 'Jefferson'.

Much work has also been done into the selection of disease-resistant Asiatic species and cultivars.[15][16]

In Europe, it is the unique example of the European White Elm Ulmus laevis which has received the most attention. Whilst this elm has little innate resistance to Dutch elm disease, it is not favoured by the vector bark beetles and thus only becomes colonized and infected when there are no other choices, a rare situation in western Europe. Research in Spain has suggested that it may be the presence of a triterpene, alnulin, which makes the tree bark unattractive to the beetle species that spread the disease.[17] However this possibility has not been conclusively proven.[18]

Hybrid cultivars[edit]

Owing to their innate resistance to Dutch elm disease, Asiatic species have been crossed with European species, or with other Asiatic elms, to produce trees which are both highly resistant to disease and tolerant of native climates. After a number of false dawns in the 1970s, this approach has produced a range of reliable hybrid cultivars now commercially available in North America and Europe.[19][20][21][22][23][24][25]

However, some of these cultivars, 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 Elm and English Elm were prized. Moreover, several exported to northwestern Europe have proven unsuited to the maritime climate conditions there, notably because of their intolerance of anoxic conditions resulting from ponding on poorly drained soils in winter. Dutch hybridizations invariably included the Himalayan Elm U. wallichiana as a source of anti-fungal genes and have proven more tolerant of wet ground; they should also ultimately reach a greater size. A number of highly resistant Ulmus cultivars has been released since 2000, notably 'Morfeo'.[20]

Cautions regarding novel cultivars[edit]

Elms take many decades to grow to maturity, and as the introduction of these disease-resistant cultivars is relatively recent, their long-term performance and ultimate size and form cannot be predicted with certainty. The National Elm Trial in North America, begun in 2005, is a nationwide trial to assess strengths and weaknesses of the 19 leading cultivars raised in the USA over a ten-year period; European cultivars have been excluded. Meanwhile, in Europe, American and European cultivars are being assessed in field trials started in 2000 by the UK charity Butterfly Conservation.[26]

The ball-headed graft narvan elm, Ulmus minor 'Umbraculifera', cultivated in Persia and widely planted in central Asia (Photo: Ronnie Nijboer)
Lafayette Street, Salem, Massachusetts: an example of the 'high-tunnelled effects' of Ulmus americana avenues once common in New England

Uses of elms in landscaping[edit]

Camperdown elm (Ulmus glabra 'Camperdown'), cultivated in Prospect Park, Brooklyn, New York
An avenue of elm trees in Fitzroy Gardens, Melbourne

One of the earliest of ornamental elms was the ball-headed graft narvan elm, Ulmus minor 'Umbraculifera', cultivated from time immemorial in Persia as a shade tree and widely planted in cities through much of south-west and central Asia. From the 18th century to the early 20th century, elms were among the most widely planted ornamental trees in both Europe and North America. They were particularly popular as a street tree in avenue plantings in towns and cities, creating high-tunnelled effects. Their tolerance of air-pollution and the comparatively rapid decomposition of their leaf-litter in the fall were further advantages. In North America, the species most commonly planted was the American elm (Ulmus americana), which had unique properties that made it ideal for such use: rapid growth, adaptation to a broad range of climates and soils, strong wood, resistance to wind damage, and vase-like growth habit requiring minimal pruning. In Europe, the wych elm (U. glabra) and the smooth-leaved elm (U. minor var. minor) were the most widely planted in the countryside, with the former in northern areas including Scandinavia and northern Britain), and the latter further south. The hybrid between these two, Dutch elm (U. × hollandica), occurs naturally and was also commonly planted. In much of England, it was the English elm (Ulmus procera) which later came to dominate the horticultural landscape. Most commonly planted in hedgerows, the English elm sometimes occurred in densities of over 1000 per square kilometre. In Australia, large numbers of English elms, as well as other species and cultivars, were planted as ornamentals following their introduction in the 19th century. From about 1850 to 1920, the most prized small ornamental elm in parks and gardens was the Camperdown elm (Ulmus glabra 'Camperdownii'), a contorted weeping cultivar of the Wych Elm grafted onto a non-weeping elm trunk to give a wide, spreading and weeping fountain shape in large garden spaces.

During the 18th and 19th centuries, elm cultivars enjoyed much popularity as ornamentals in Europe by virtue of their rapid growth and variety of foliage and forms.[27] This "belle époque" lasted until the First World War, when the consequences of hostilities, notably in Germany whence at least 40 cultivars originated, and the outbreak of Dutch elm disease saw the elm slide into horticultural decline. The devastation caused by the Second World War, and the demise in 1944 of the huge Späth nursery in Berlin, only accelerated the process. The outbreak of the new, three times more virulent, strain of Dutch elm disease Ophiostoma novo-ulmi in the late 1960s brought the tree to its nadir.

Since circa 1990 however, the elm has enjoyed a renaissance through the successful development in North America and Europe of cultivars highly resistant to the new disease.[2] Consequently, the total number of named cultivars, ancient and modern, now exceeds 300, although many of the older clones, possibly over 120, have been lost to cultivation. Enthusiasm for the newer clones often remains low owing to the poor performance of earlier, supposedly disease-resistant Dutch trees released in the 1960s and 1970s. In the Netherlands, sales of elm cultivars slumped from over 56,000 in 1989 to just 6,800 in 2004,[28] whilst in the UK, only four of the new American and European releases were commercially available in 2008.

Other uses of elms[edit]

Wood[edit]

Elm wood
Elm in boat-building: John Constable, Boat-building near Flatford Mill, 1815 (landscape with hybrid elms Ulmus × hollandica [1])
English longbow of elm

Elm wood was valued for its interlocking grain, and consequent resistance to splitting, with significant uses in wagon wheel hubs, chair seats and coffins. The elm's wood bends well and distorts easily making it quite pliant. The often long, straight, trunks were favoured as a source of timber for keels in ship construction. Elm is also prized by bowyers; of the ancient bows found in Europe, a large portion of them are elm. During the Middle Ages elm was also used to make longbows if yew was unavailable.

The first written references to elm occur in the Linear B lists of military equipment at Knossos in the Mycenaean Period. Several of the chariots are of elm (« πτε-ρε-ϝα », pte-re-wa), and the lists twice mention wheels of elmwood.[29] Hesiod says that ploughs in Ancient Greece were also made partly of elm.[30]

The density of elm wood varies between species, but averages around 560 kg per cubic metre.[31]

Elm wood is also resistant to decay when permanently wet, and hollowed trunks were widely used as water pipes during the medieval period in Europe. Elm was also used as piers in the construction of the original London Bridge. However this resistance to decay in water does not extend to ground contact.[31]

Viticulture[edit]

The Romans, and more recently the Italians, used to plant elms in vineyards as supports for vines. Lopped at three metres, the elms' quick growth, twiggy lateral branches, light shade and root-suckering made them ideal trees for this purpose. The lopped branches were used for fodder and firewood.[32] Ovid in his Amores characterizes the elm as "loving the vine": ulmus amat vitem, vitis non deserit ulmum (:the elm loves the vine, the vine does not desert the elm),[33] and the ancients spoke of the "marriage" between elm and vine.[34]

Medicinal products[edit]

The mucilaginous inner bark of the Slippery Elm Ulmus rubra has long been used as a demulcent, and is still produced commercially for this purpose in the United States with approval for sale as a nutritional supplement by the U.S. Food and Drug Administration.[35]

Fodder[edit]

Elms also have a long history of cultivation for fodder, with the leafy branches cut to feed livestock. The practice continues today in the Himalaya, where it contributes to serious deforestation.[36]

Biomass[edit]

As fossil fuel resources diminish, increasing attention is being paid to trees as sources of energy. In Italy, the Istituto per la Protezione delle Piante is (2012) in the process of releasing to commerce very fast growing elm cultivars, able to increase in height by more than 2 m (6 ft) per annum.[20]

Food[edit]

Elm bark, cut into strips and boiled, sustained much of the rural population of Norway during the great famine of 1812. The seeds are particularly nutritious, comprising 45% crude protein, and less than 7% fibre by dry mass.[37]

Internal mill-wheel of elm, De Hoop mill, Oldebroek, Netherlands

Alternative medicine[edit]

Elm has been listed as one of the 38 substances that are used to prepare Bach flower remedies,[38] a kind of alternative medicine promoted for its effect on health. However according to Cancer Research UK, "there is no scientific evidence to prove that flower remedies can control, cure or prevent any type of disease, including cancer".[39]

Bonsai[edit]

Chinese Elm Ulmus parvifolia bonsai

Chinese elm Ulmus parvifolia is a popular choice for bonsai owing to its tolerance of severe pruning.

Genetic resource conservation[edit]

In 1997, a European Union elm project was initiated, its aim to coordinate the conservation of all the elm genetic resources of the member states and, among other things, to assess their resistance to Dutch elm disease. Accordingly, over 300 clones were selected and propagated for testing.[40][41][42]

Notable elm trees[edit]

Many elm (Ulmus) trees of various kinds have attained great size or otherwise become particularly noteworthy; among these are the following.

American Elm Ulmus americana[edit]

William Penn and Indians with treaty under a large elm in 1683, as shown in the painting by Benjamin West
"Herbie", once New England's oldest and tallest elm, was cut in 2010 after a long battle with Dutch elm disease.
Johnstown Elm in Johnstown, NY. 196 inch circumference, 85 feet tall, disease free as of Sept., 2013. Largest elm in NY, photo Jan. 2012

Most of North America's notable elms are Ulmus americana, a fast-growing and long-lived species capable of attaining great size in a few centuries, especially when open-grown.[7]

Wych Elm Ulmus glabra[edit]

L'Olmo di Mergozzo, Piedmont (Ulmus minor), present in 1600 and still standing today

Dutch Elm Ulmus × hollandica[edit]

Field Elm Ulmus minor[edit]

The Biscarrosse Elm, France, Field Elm (Ulmus minor) planted 1350, died 2010.

English Elm Ulmus procera[edit]

The 'Preston Twins', English elms in Brighton, England

Other, unidentified elms[edit]

The elm in art[edit]

Many artists have admired elms for the ease and grace of their branching and foliage, and have painted them with sensitivity. Elms are a recurring element in the landscapes and studies of, for example, John Constable, Ferdinand Georg Waldmüller, Frederick Childe Hassam, Karel Klinkenberg,[79] and George Inness.

The elm in mythology and literature[edit]

Achilles and Scamander
Dryad

In Greek mythology the nymph Ptelea (Πτελέα, Elm) was one of the eight Hamadryads, nymphs of the forest and daughters of Oxylos and Hamadryas.[80]

The first reference in literature to elms occurs in the Iliad. When Eetion, father of Andromache, is killed by Achilles during the Trojan War, the Mountain Nymphs plant elms on his tomb («περὶ δὲ πτελέoι εφύτεψαν νύμφαι ὀρεστιάδες, κoῦραι Διὸς αἰγιόχoιo»).[81] Also in the Iliad, when the River Scamander, indignant at the sight of so many corpses in his water, overflows and threatens to drown Achilles, the latter grasps a branch of a great elm in an attempt to save himself («ὁ δὲ πτελέην ἕλε χερσὶν εὐφυέα μεγάλην».[82]

The Nymphs also planted elms on the tomb in the Thracian Chersonese of “great-hearted Protesilaus’’ («μεγάθυμου Πρωτεσιλάου»), the first Greek to fall in the Trojan War. These elms grew to be the tallest in the known world; but when their topmost branches saw far off the ruins of Troy, they immediately withered, so great still was the bitterness of the hero buried below, who had been loved by Laodamia and slain by Hector.[83][84][85] The story is the subject of a poem by Antiphilus of Byzantium (1st century A.D.) in the Palatine Anthology:

Θεσσαλὲ Πρωτεσίλαε, σὲ μὲν πολὺς ᾄσεται αἰών,
Tρoίᾳ ὀφειλoμένoυ πτώματος ἀρξάμενoν•
σᾶμα δὲ τοι πτελέῃσι συνηρεφὲς ἀμφικoμεῦση
Nύμφαι, ἀπεχθoμένης Ἰλίoυ ἀντιπέρας.
Δένδρα δὲ δυσμήνιτα, καὶ ἤν ποτε τεῖχoς ἴδωσι
Tρώϊον, αὐαλέην φυλλοχoεῦντι κόμην.
ὅσσoς ἐν ἡρώεσσι τότ᾽ ἦν χόλoς, oὗ μέρoς ἀκμὴν
ἐχθρὸν ἐν ἀψύχoις σώζεται ἀκρέμoσιν.[86]
[:Thessalian Protesilaos, a long age shall sing your praises,
Of the destined dead at Troy the first;
Your tomb with thick-foliaged elms they covered,
The nymphs, across the water from hated Ilion.
Trees full of anger; and whenever that wall they see,
Of Troy, the leaves in their upper crown wither and fall.
So great in the heroes was the bitterness then, some of which still
Remembers, hostile, in the soulless upper branches.]

Protesilaus had been king of Pteleos (Πτελεός) in Thessaly, which took its name from the abundant elms (πτελέoι) in the region.[87]

Elms occur often in Pastoral Poetry, where they symbolise the idyllic life, their shade being mentioned as a place of special coolness and peace. In the first Idyll of Theocritus, for example, the goat-herd invites the shepherd to sit “here beneath the elm” («δεῦρ’ ὑπὸ τὰν πτελέαν») and sing. Beside elms Theocritus places “the sacred water” («το ἱερὸν ὕδωρ») of the Springs of the Nymphs and the shrines to the nymphs.[88]

Aside from references literal and metaphorical to the elm and vine theme, the tree occurs in Latin literature in the Elm of Dreams in the Aeneid.[89] When the Sibyl of Cumae leads Aeneas down to the Underworld, one of the sights is the Stygian Elm:

In medio ramos annosaque bracchia pandit
ulmus opaca, ingens, quam sedem somnia vulgo
uana tenere ferunt, foliisque sub omnibus haerent.
[:Spreads in the midst her boughs and agéd arms
an elm, huge, shadowy, where vain dreams, 'tis said,
are wont to roost them, under every leaf close-clinging.]

Virgil refers to a Roman superstition (vulgo) that elms were trees of ill-omen because their fruit seemed to be of no value.[90] It has been noted [91] that two elm-motifs have arisen from classical literature: (1) the 'Paradisal Elm' motif, arising from pastoral idylls and the elm-and-vine theme, and (2) the 'Elm and Death' motif, perhaps arising from Homer's commemorative elms and Virgil's Stygian Elm. Many references to elm in European literature from the Renaissance onwards fit into one or other of these categories.

There are two examples of pteleogenesis (:birth from elms) in world myths. In Germanic and Scandinavian mythology the first woman, Embla, was fashioned from an elm,[92] while in Japanese mythology Kamuy Fuchi, the chief goddess of the Ainu people, "was born from an elm impregnated by the Possessor of the Heavens".[93]

The elm occurs frequently in English literature, one of the best known instances being in Shakespeare's A Midsummer Night's Dream, where Titania, Queen of the Fairies, addresses her beloved Nick Bottom using an elm-simile. Here, as often in the elm-and-vine motif, the elm is a masculine symbol:

Sleep thou, and I will wind thee in my arms.
... the female Ivy so
Enrings the barky fingers of the Elm.
O, how I love thee! how I dote on thee! [94]

Another of the most famous kisses in English literature, that of Paul and Helen at the start of Forster's Howards End, is stolen beneath a great wych elm.

The Elm Tree is also referenced in children's literature. An Elm Tree and Three Sisters is a children's book about three young sisters that plant a small elm tree in their backyard. Throughout the years, the sisters begin to realize that the elm tree becomes an integral part of their lives. The sisters see that the elm tree has been with them through many important milestones through life and they grow old with the tree.

[95]

The elm in politics[edit]

The Cutting of the elm was a diplomatic altercation between the Kings of France and England in 1188, during which an elm tree near Gisors in Normandy was felled.

In politics the elm is associated with revolutions. In England after the Glorious Revolution of 1688, the final victory of parliamentarians over monarchists, and the arrival from Holland, with William & Mary, of the 'Dutch Elm' hybrid, planting of this cultivar became a fashion among enthusiasts of the new political order.[3][96]

In the American Revolution 'The Liberty Tree' was an American white elm in Boston, Massachusetts, in front of which, from 1765, the first resistance meetings were held against British attempts to tax the American colonists without democratic representation. When the British, knowing that the tree was a symbol of rebellion, felled it in 1775, the Americans took to widespread 'Liberty Elm' planting, and sewed elm symbols on to their revolutionary flags.[97][98] Elm-planting by American Presidents later became something of a tradition.

In the French Revolution, too, Les arbres de la liberté (:Liberty Trees), often elms, were planted as symbols of revolutionary hopes - the first in Vienne, Isère, in 1790, by a priest inspired by the Boston elm.[97] L'Orme de La Madeleine (:the Elm of La Madeleine), Faycelles, Département de Lot, planted around 1790 and surviving to this day, was a case in point.[99] By contrast, a famous Parisian elm associated with the Ancien Régime, L’Orme de Saint-Gervais in the Place St-Gervais, was felled by the revolutionaries; church authorities planted a new elm in its place in 1846, and an early 20th-century elm stands on the site today.[100] Premier Lionel Jospin, obliged by tradition to plant a tree in the garden of the Hôtel Matignon, the official residence and workplace of Prime Ministers of France, insisted on planting an elm, so-called 'tree of the Left', choosing the new disease-resistant hybrid 'Clone 762' (Ulmus 'Wanoux' = Vada).[101]

Liberty Elms were also planted in other countries in Europe to celebrate their revolutions, an example being L'Olmo di Montepaone, L'Albero della Libertà (:the Elm of Montepaone, Liberty Tree) in Montepaone, Calabria, planted in 1799 to commemorate the founding of the democratic Parthenopean Republic, and surviving till it was brought down by a recent storm (it has since been cloned and 'replanted').[102] And after the Greek Revolution of 1821-32, a thousand young elms were brought to Athens from Missolonghi, "Sacred City of the Struggle" against the Turks and scene of Lord Byron's death, and planted in 1839-40 in the National Garden.[103][104] In Thessaloniki a more recent Libery Elm, «Η Φτελιά της 25ης Μαρτίου» (:The Elm of the 25th March), the oldest elm in the city, still stands at the beginning of 25 March Street (Οδός 25ης Μαρτίου), date of the beginning of the 1821 revolution.[105][106] In an ironic development, wild elms have spread and taken over the grounds of the abandoned Greek royal summer palace at Tatoi in Attica.

The propagation of elms[edit]

A rooted cutting of European White Elm (July)

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.[1] 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 one centimetre, and germinate in three weeks. Slow-germinating American Elm will remain dormant until the second season.[107] Seeds from autumn-flowering elms ripen in the Fall and germinate in the spring.[107] 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 Ulmus procera in England, 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,[108] taking root-cuttings in early spring; taking softwood cuttings in early summer;[109] grafting; layering; and micropropagation. A bottom heat of 18 degrees [110] and humid conditions are maintained for hard- and softwood cuttings. The transplanting of root-suckers remains the easiest and commonest propagation-method for European Field Elm and its hybrids. For 'specimen' urban elms, grafting to wych-elm root-stock 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 2 – 3 m, 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 on this species.[111]

Organisms associated with elm[edit]

See also[edit]

References[edit]

  1. ^ a b c d e f g h i Richens, R. H. (1983). Elm. Cambridge University Press.
  2. ^ a b 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. ISBN 9789050112819
  3. ^ a b Rackham, O. (1980). Ancient woodland: its history, vegetation and uses. Edward Arnold, London
  4. ^ Bean, W. J. (1981). Trees and shrubs hardy in Great Britain, 7th edition. Murray, London
  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.
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Monographs[edit]

Further reading[edit]

External links[edit]