Ulmus L. (1753), the elm, contains around 30 species from around the northern hemisphere, in the family Ulmaceae. Description Trees to 35m, or rarely shrubs, often suckering and regenerating from the roots. The leaves are alternate, usually deciduous, toothed, with pinnate veins, asymmetric at the base, and sometimes rough on the surface. The flowers are small, in short-stemmed bunches borne on bare twigs before the leaves, usually in spring. Sepals 5–9, fused at the base; petals absent. Stamens 3–9, the anthers usually red before they open. Carpel 1, with a deeply 2-lobed style. Pollination is by wind. The fruits are 1-seeded samaras surrounded by thin wings. Key Recognition Features The rough, toothed leaves with pinnate veins, and in spring the small flowers along the branches, followed by the green, winged fruits. Evolution and Relationships Ulmaceae contains 18 genera, some tropical. It is usually grouped with the Urticales, which includes the Urticaceae, Cannabaceae, and Moraceae; there are also similarities with the Eucommiaceae. Two subfamilies are recognised; Ulmoideae (Ulmus, Zelkova, Hemiptelea, Planera Gmel.) with dry fruits, and 2n=28; Celtidoidae (Aphananthe, Celtis, Trema Lour.) with fleshy fruits and 2n=20, 30, and 40. Ecology and Geography In woods and in hedgerows, nowadays often shrubby as large trees have been killed by disease in many areas. Six species are native in North America; the rest mainly in China. The wych elm, U. glabra Huds., is less susceptible to disease, and common in northern areas. Ulmus americana L. has also survived in many areas. Comment Virgil described how grape vines were trained on elms, and this practice could until recently be seen in the countryside near Naples. The timber was used for piles and for wooden water pipes and drain pipes, because it is resistant to rot in wet conditions. Elms are common in hedgerows throughout southern England, and in parts of North America, being fast growing and often planted for shade, shelter, fodder, and firewood. Until the 1960s they were fine trees, a conspicuous feature of the landscape in lowland areas, but from 1965 onwards a virulent strain of Dutch elm disease, Ceratocystus ulmi, appeared and was spread quickly by elm bark beetles, Scolytus spp., and now hardly a single large tree remains. Dead trees often resprout and reach around 6m before succumbing to disease again. Many North American species are also affected by the disease, which reached America around 1930. This is not the first time that disease has decimated European elms; elm pollen is common in late post-glacial peats in southern England, but around 4000bc, about the time of the coming of Neolithic agriculture, about half the trees suddenly died. Other less devastating epidemics killed large numbers of European elms around 1500, in 1820–60, and in 1918–30. |
