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Elm: the story on HearLore | HearLore
Elm
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the family Ulmaceae, yet their story begins not with their grandeur but with their microscopic seeds. These seeds, known as samarae, are so light that a single pound of British elm seeds contains approximately 50,000 individual units, each capable of traveling vast distances on the wind. This biological strategy allowed elms to colonize the Northern Hemisphere, from the temperate zones of North America and Eurasia to the tropical-montane regions of Southeast Asia and even as far south as Iran and Libya. Despite their wide distribution, the elm is a hermaphroditic species with apetalous perfect flowers that rely entirely on wind pollination, a trait that distinguishes them from many of their flowering relatives. The leaves of the elm are alternate and typically doubly serrate, often asymmetric at the base and acuminate at the apex, creating a distinctive silhouette that has been recognized by botanists for centuries. The fruit itself is a round samara flushed with chlorophyll, a rare adaptation that allows it to perform photosynthesis before the leaves even emerge, ensuring the seed has energy to germinate immediately upon landing. This biological efficiency has allowed elms to thrive in diverse environments, from the saline deposits of coastal Britain to the dry soils of the Himalayas, making them one of the most critical genera in the entire British flora.
The Botanical Mystery
Identifying an elm tree is a task that has baffled scientists for centuries, leading to the creation of a specialized field of study known as pteleology. The genus Ulmus contains between 30 to 40 species, but the exact number remains ambiguous due to the ease with which elms hybridize and the development of local seed-sterile vegetatively propagated microspecies. This taxonomic confusion is so profound that botanist Oliver Rackham described species and varieties as a distinction in the human mind rather than a measured degree of genetic variation. The oldest fossils of Ulmus are leaves dating back to the Paleocene epoch, found across the Northern Hemisphere, indicating that these trees have been a part of the Earth's ecosystem for millions of years. Despite their ancient lineage, elms are distantly related to cannabis, mulberries, figs, hops, and nettles, belonging to the urticalean rosid clade. The classification of elms has evolved over three centuries, with a large number of synonyms accumulating until the current accepted names were established by Brummitt. This complexity is further compounded by the fact that many species are endemic to specific regions, with eight species native to North America, three to Europe, and approximately two dozen found in Asia. The difficulty in delineating species has led to a situation where the true diversity of the elm genus remains a subject of intense debate among pteleologists, who argue over identification and classification with the same fervor as any other botanical mystery.
Common questions
What is the scientific classification of the elm tree?
Elms are deciduous and semi-deciduous trees comprising the genus Ulmus in the family Ulmaceae. They belong to the urticalean rosid clade and are distantly related to cannabis, mulberries, figs, hops, and nettles.
How many seeds are in a pound of British elm seeds?
A single pound of British elm seeds contains approximately 50,000 individual units. These seeds are known as samarae and are so light that they can travel vast distances on the wind.
When did Dutch elm disease first arrive in Europe?
The fungus Ophiostoma ulmi arrived in Europe from Asia in 1910. It was first described in the 1920s by Dutch botanists Bea Schwarz and Christina Johanna Buisman.
What are the primary uses of elm wood in history?
Elm wood has been valued for its interlocking grain and resistance to splitting, making it a material of choice for wagon-wheel hubs, chair seats, and coffins. The wood was also used for keels in ship construction and as water pipes during the medieval period in Europe.
Which elm tree was used as a symbol during the American Revolution?
The Liberty Tree was an American white elm in Boston, Massachusetts, in front of which the first resistance meetings were held against British attempts to tax the American colonists from 1765. When the British felled it in 1775, the Americans took to widespread Liberty Elm planting and sewed elm symbols on to their revolutionary flags.
When did efforts to develop Dutch elm disease resistant cultivars begin in the Netherlands?
Efforts to develop DED-resistant cultivars began in the Netherlands in 1928 and continued, uninterrupted by World War II, until 1992. Research has followed two paths involving species and species cultivars, and hybrid cultivars.
The history of the elm in the 20th century is defined by a catastrophic event known as Dutch elm disease, which devastated elms throughout Europe and much of North America. The disease derives its name from the first description of the cause in the 1920s by Dutch botanists Bea Schwarz and Christina Johanna Buisman, who identified a microfungus transmitted by two species of Scolytus elm-bark beetles. The fungus, Ophiostoma ulmi, arrived in Europe from Asia in 1910 and was accidentally introduced to North America in 1928, causing steady destruction until it was weakened by viruses and disappeared by the 1940s. However, a second, far more virulent strain, Ophiostoma novo-ulmi, appeared in the United States in the 1940s and 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. This new strain rapidly eradicated most of the mature elms from western Europe, and a second subspecies caused similar devastation in Eastern and Central Europe. The disease affects all species of elms native to North America and Europe, but many Asiatic species have evolved antifungal genes and are resistant. The tree responds to the infection by producing tyloses, effectively blocking the flow from roots to leaves, leading to the death of the tree. 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, leaving the elm in a state of perpetual vulnerability.
The Wood of Kings and Ships
Elm wood has been valued for its interlocking grain and consequent resistance to splitting, making it a material of choice for wagon-wheel hubs, chair seats, and coffins. The density of elm wood varies between species but averages around 560 kg/m3, providing a balance of strength and flexibility that has been sought after for millennia. The bodies of Japanese Taiko drums are often cut from the wood of old elm trees, as the wood's resistance to splitting is highly desired for nailing the skins to them, and a set of three or more is often cut from the same tree. The elm's wood bends well and distorts easily, making it ideal for the often long, straight trunks that were favored 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 are elm, and during the Middle Ages, elm was 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, where several of the chariots are of elm, and the lists twice mention wheels of elmwood. The 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, but this resistance to decay in water does not extend to ground contact, limiting its use in certain applications.
The Vine and The Revolution
The elm has played a significant role in human history, from its use as supports for vines in Roman vineyards to its association with political revolutions. The Romans and, more recently, Italians planted elms in vineyards as supports for vines, lopped at 3 meters, with the elm's quick growth, twiggy lateral branches, light shade, and root suckering making them ideal trees for this purpose. The lopped branches were used for fodder and firewood, and the elm was characterized by Ovid as loving the vine, with the ancients speaking of the marriage between elm and vine. In politics, the elm is associated with revolutions, from the cutting of the elm in 1188 during a diplomatic altercation between the kings of France and England to the planting of Liberty Trees 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 felled it in 1775, the Americans took to widespread Liberty Elm planting, and sewed elm symbols on to their revolutionary flags. In the French Revolution, Les arbres de la liberté, often elms, were planted as symbols of revolutionary hopes, the first in Vienne, Isère, in 1790, by a priest inspired by the Boston elm. The elm tree is also referenced in children's literature and has been used as a symbol of rebellion and hope in various political contexts.
The Mythic Roots
Elms have deep roots in mythology and literature, appearing in Greek mythology as the nymph Ptelea, one of the eight hamadryads, and in the Iliad, where mountain nymphs planted elms on the tomb of Eetion, father of Andromache. The elm also appears in the Iliad when the River Scamander, indignant at the sight of so many corpses in his water, overflows and threatens to drown Achilles, who grasps a branch of a great elm in an attempt to save himself. The elm is also referenced in the Aeneid, where the Sibyl of Cumae leads Aeneas down to the Underworld, and one of the sights is the Stygian Elm, a huge, shadowy tree where vain dreams are wont to roost. The elm occurs often in pastoral poetry, where it symbolizes the idyllic life, its shade being mentioned as a place of special coolness and peace. In English literature, the elm is one of the best known instances, appearing in Shakespeare's A Midsummer Night's Dream, where Titania, Queen of the Fairies, addresses her beloved Nick Bottom using an elm-simile. The elm is also referenced in the story of Protesilaus, the first Greek to fall in the Trojan War, whose tomb was planted with elms that grew to be the tallest in the known world, but withered when their topmost branches saw the ruins of Troy. The elm has also been used as a symbol of rebellion and hope in various political contexts, from the Liberty Trees of the American Revolution to the Elm of La Madeleine in France.
The Renaissance of Resilience
Since around 1990, the elm has enjoyed a renaissance through the successful development in North America and Europe of cultivars highly resistant to Dutch elm disease. Efforts to develop DED-resistant cultivars began in the Netherlands in 1928 and continued, uninterrupted by World War II, until 1992, with similar programs initiated in North America, Italy, and Spain. Research has followed two paths: species and species cultivars, and hybrid cultivars. In North America, careful selection has produced a number of trees resistant not only to DED, but also to the droughts and cold winters that occur on the continent. Research in the United States has concentrated on the American elm, resulting in the release of DED-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. In Europe, the European white elm has received much attention, and more recently, field elms highly resistant to DED have been discovered in Spain, forming the basis of a major breeding programme. The elm's wood is also being used as a source of energy, with fast-growing elm cultivars being released to commerce in Italy, able to increase in height by more than 1 meter per year. The elm has also been used as a source of food, with elm bark, cut into strips and boiled, sustaining much of the rural population of Norway during the great famine of 1812. The seeds are particularly nutritious, containing 45% crude protein, and less than 7% fiber by dry mass, making them a valuable resource in times of scarcity.