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 and Iran; its northern outposts are the Baltic islands of Öland and Gotland, although it may have been introduced by humans. 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. Current treatment of the species owes much to Richens, who noted (1983) that several varieties of field elm are distinguishable on the European mainland. Of these, he listed the small-leaved U. minor of France and Spain; the narrow-leaved U. minor of northern and central Italy; the densely hairy leaved U. minor of southern Italy and Greece; the U. minor with small-toothed leaves from the Balkans; the U. minor with large-toothed leaves from the Danube region; and the small-leaved U. minor from southern Russia and Ukraine. As for British varieties, "the continental populations most closely related [to eastern English Field Elm] are in central Europe", while south-western forms were introduced from France. He concluded, however, that owing to incomplete field-research at the time of writing, it was "not possible to present an overall breakdown of the European Field Elm into regional varieties". The epithet 'red' elm was commonly used by British foresters, an allusion to the colour of the timber. Richens sank a number of British elms, notably English elm, as either subspecies or varieties of U. minor in 1968. However, Melville, writing ten years later, identified five distinct species (including U. glabra in the count), several varieties and numerous complex hybrids. In 1992 Armstrong identified no fewer than forty British species and microspecies. Clive Stace (1997) wrote of the British elms "The two-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. In 2009 Dr Max Coleman of the Royal Botanic Garden, Edinburgh wrote: "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. This means that enigmatic British elms such as Plot elm and English elm have been shown 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." It is hoped that analysis of molecular markers will ultimately eliminate the taxonomic confusion.
Description The tree typically grows to < 30 m (98 ft) and bears a rounded crown. The bark of the trunk is rough, furrowed lightly in older trees to form a block pattern. Young branchlets occasionally have corky wings. The shoots are slender compared with those of wych elm. 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. The samarae are oval or obovate, glabrous, 12–15 mm (15⁄32–19⁄32 in) long, notched at the top, with the seed close to the notch. Ulmus minor in France generally begins to flower and fruit when aged 10 years. The species readily produces suckers from roots and stumps, even after devastation by Dutch elm disease; consequently genetic resources are not considered endangered.
Pests and diseases The species has a hugely variable reaction to Dutch elm disease (DED), including all the fashionable pre-20th century plantsman's clones (see Subspecies and varieties). However, field elm is genetically highly variable; Italian specimens when inoculated with the pathogen displayed between 15 and 100% dieback and between 70 and 100% wilting. Tolerance of elm yellows (phloem necrosis) is generally good, U. minor exhibiting symptoms such as the 'witch's broom' only sporadically throughout Italy, including Sicily and Sardinia, however the disease was often locally common within the species in France, including Paris.
Cultivation U. minor in general and a number of clones in particular (see 'Cultivars' below) were once commonly cultivated across Europe in town and country, but owing to its susceptibility to Dutch elm disease, U. minor is now uncommon in cultivation. However, in an ongoing project that began in the 1990s, several thousand surviving field elms have been tested for innate resistance by national research institutes in the EU, with a view to returning field elm to cultivation. Results from Spain (2013), for example, confirm that a very small number of surviving field elms (about 0.5% of those tested) appear to have comparatively high levels of tolerance of the disease, and it is hoped that a controlled crossing of the best of these will produce resistant Ulmus minor hybrids for cultivation. In the UK, despite its late leaf-flush in the north and its suckering habits, continental U. minor was occasionally planted as an ornamental urban tree. Augustine Henry wrote in 1913 that “In all probability many of” the U. minor planted in parks in Scotland were of French origin. More recently U. minor seed was imported to the UK from Italy. There are mature survivors in Edinburgh that are not the common U. minor cultivars (2015). U. minor was introduced, as U. campestris suberosa or simply U. suberosa, to the US and Canada, where a few old specimens survive, and to the southern hemisphere, notably Australasia and Argentina.
… excerpt ends here. Continue reading the full article.
