| Ulmus minor | |
|---|---|
| Field Elm, Blismes, Nièvre, France.
Photo: Eric Collin, Cemagref, 2007. |
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| Scientific classification | |
| Kingdom: | Plantae |
| Division: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Rosales |
| Family: | Ulmaceae |
| Genus: | Ulmus |
| Species: | U. minor |
| Binomial name | |
| Ulmus minor Mill. |
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| Synonyms | |
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Ulmus minor Mill., the Field Elm, is by far the most polymorphic of the European species, although its taxonomy remains a matter of contention. Its natural range is predominantly south European, extending to Asia Minor; its northern outposts are the Baltic islands of Öland and Gotland,[1] although it may have been introduced here by man. The tree's typical habitat is low-lying forest along the main rivers, growing in association with oak and ash, where it tolerates summer floods as well as droughts.[2] Current treatment of the species owes much to Richens,[3] who sank a number of British elms as either subspecies or varieties in 1968. However, Melville,[4] writing 10 years later, identified five distinct species, several varieties and numerous complex hybrids. In 1992, 14 years after Melville, Armstrong [5] identified no fewer than 40 species and microspecies. Stace (1997) wrote of the British elms "The 2-species (glabra and minor) concept of Richens is not sufficiently discriminating to be of taxonomic value". Nevertheless, it is Richens’ classification which has been the most commonly adopted in recent years, although it is not used in Flora Europaea [14].[6]
Moreover, Dr Max Coleman of the Royal Botanic Garden, Edinburgh wrote (2009): "The advent of DNA fingerprinting has shed considerable light on the question. A number of studies have now shown that the distinctive forms Melville elevated to species and Richens lumped together as field elm are single clones, all genetically identical, which have been propagated by vegetative means such as cuttings or root suckers. Ergo: enigmatic British elms such as Plot's Elm and English Elm have been shewn to be single clones of Field Elm. Although Richens did not have the evidence to prove it, he was correct in recognising a series of clones and grouping them together as a variable species." [7]
It is hoped that analysis of molecular markers will ultimately eliminate the taxonomic confusion.
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The tree typically grows to < 30 m and bears a rounded crown.[8] The bark of the trunk is rough, furrowed lightly in older trees to form a block pattern. Young branchlets occasionally have corky wings. The leaves are smaller than those of the other European species, hence the specific epithet minor, however they can vary greatly according to the maturity of the tree. Leaves on juvenile growth (suckers, seedlings etc.) are coarse and pubescent, whereas those on mature growth are generally smooth, though remaining highly variable in form; there are generally fewer than 12 pairs of side veins. A common characteristic is the presence of minute black glands along the leaf veins, detectable with the aid of a magnifying glass.[2] The samarae are typically ovate and notched, the notch extending to the central seed.
The species readily produces suckers from roots and stumps, even after devastation by Dutch elm disease, consequently genetic resources are not considered endangered [15].
Most trees are very susceptible to Dutch elm disease.
Owing to its susceptibility to Dutch elm disease, U. minor is now uncommon in cultivation.
An ancient Field Elm stood until recently in the village square of Metaxades, Thrace, Greece [16]. Having abandoned their original village in 1286 after cholera outbreaks, the villagers re-founded it in the hills where a young elm was growing beside a spring. An elm (reputedly the original) and the fountain have been the focal-point of the village ever since.[9][10] A tree reputedly over 650 years old survived in the centre of Biscarrosse south of Bordeaux until the summer of 2010, when it finally succumbed to Dutch elm disease. [17] [18] [19] Another veteran with a 6-metre girth survives at Bettange, France, close to the Belgian border, reputedly planted in 1593 [20] [21]. A tree approximately 400 years old and 5.55 metres in girth grows in the town of Mergozzo in Piedmont, Italy. [22] 'L'olmo di Mergozzo', like its French counterparts 'l'orme de Biscarosse' and 'l’orme de Bettange', is hollowed out by age, its life prolonged by lopping. Another hollow veteran is the elm in the Plaza del Olmo in Navajas, Valencia, 6.3 metres in girth, planted in 1636 and featuring on the town crest.[11] Rare examples of centuries-old Field Elms that retain their heartwood and crowns are the majestic 360-year old specimen in the village square of Strinylas, Corfu [23],[12][13] and an immemorial elm opposite the village square of Aidona in Thessaly, Greece [24],[14] which has been "listed" as a national "Monument of Nature".[15] Trees reputedly even older (200 cm d.b.h.) can be found in Bulgaria near Sliven in the village of Zhelyo voevoda.
In the UK, despite its late leaf-flush in the north and its suckering habits, Ulmus minor was occasionally planted as an ornamental urban tree. Among mature survivors in Edinburgh (2010) are a fine specimen in the grounds of Holyrood Palace, opposite Abbeyhill Crescent, another in the forecourt of the Royal Forth Yacht Club, Boswall Road, and a third on the corner of Abbey Mount and Regent Road. Augustine Henry says that the U. minor planted in parks in Scotland were of French origin.[16]
Numerous cultivars have been raised in Europe since the 18th century, although most are now probably extinct owing to the ravages of Dutch elm disease:
The tree's natural range generously overlaps that of Wych Elm Ulmus glabra to the north, and readily hybridizes with it to produce the so-called 'Dutch Elm' Ulmus × hollandica, while in Spain it has also naturally hybridized with the Siberian Elm U. pumila introduced in the 16th century.
The tree has featured strongly in artificial hybridization experiments in Europe and to a lesser extent in the USA. Most of the European research was based at Wageningen in the Netherlands until 1992, whence a number of hybrid cultivars have been commercially released since 1960. The earlier trees were raised in response to the initial Dutch elm disease pandemic that afflicted Europe after the First World War, and were to prove vulnerable to the much more virulent strain of the disease that arrived in the late 1960s. However, further research eventually produced several trees effectively immune to disease which were released after 1989.[17]
A form of U. minor not uncommon in central Europe, and sufficiently distinct to be recognised by some continental botanists as a variety, is the so-called korkulme (Germany), korkelm (Denmark), or wiąz korkowa (Poland) - U. minor var. suberosa ((Moench) Rehder), the 'Cork-barked elm' of A. Henry, who says it "appears to be a common variety in the forests of central Europe".[18] Elwes and Henry, having seen specimens in Slavonia, Croatia, and in Gisselfelde, Denmark, as well as at Kew, describe it as having "branchlets of the second to the tenth year furnished with corky wings", but with "leaves and samarae as in the type". W. J. Bean reports it "to be often rather dwarf and to occur in dry habitats".[19]
A fine specimen so labelled, with thick corky branchlets giving a dense winter silhouette, stands in the Botanic Gardens of Visby in Gotland, Sweden,[20] and others are found in the University of Copenhagen Arboretum [21] and in the Alexandru Buia Botanic Garden in the University of Craiova, Rumania.[22][23][24]
R. H. Richens regarded the tree as undifferentiated U. minor, not distinct enough to merit varietal status, and the name a relic of taxonomic conservatism.[25]
None known
