Elms are deciduous trees of the genus Ulmus, family Ulmaceae, native to temperate regions of the Northern Hemisphere.

Leaves

Elm leaves are deciduous and alternate in two rows along the shoot. The shape is oval and tapers towards a point. The edge is ragged and saw-toothed and veins are prominent. The size is dependent on the species, but the leaves of an American elm are usually between 10 and 15 cm in length.

Bark

Bark of an American elm The bark of an American elm is dark grayish-brown becoming mottled ash-gray as the tree ages. The surface is deeply furrowed with broad obliquely intersecting ridges.

Fruit

The fruit is a round samara. A samara is a type of fruit in which a flattened wing of fibrous, papery tissue develops from the ovary wall.

Habitat

Elm trees grow naturally in river valleys throughout the province and are thus able to survive the natural stresses of limited precipitation, cold winters and hot summers. In addition to natural stresses, American elms are better able most other species to withstand the stresses placed on trees in populated locations: eg. trampling, pruning and shaping to ensure visibility, and pollution.

Uses

Elm wood is valued for its interlocking grain, and consequent resistance to splitting, with significant uses in chair seats and coffins. The wood is also resistant to decay when permanently wet, and was used for making water pipes during the mediaeval period in Europe. Elms also have a long history of cultivation for fodder, with the leafy branches cut for livestock. The bark, cut into strips and boiled, sustained much of the rural population of Norway during the famine in the mid-19th century.

Notes

Dutch elm disease has devastated elms throughout Europe and North America. It is caused by the micro- fungus Ophiostoma novo-ulmi 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 anti-fungal genes and are resistant. Fungal spores, introduced into wounds in the tree caused by the beetles, germinate in the vascular system, 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 of over three hundred clones of the three European species with the fungus failed to find a single variety possessed of any significant resistance.