Ulmus (Elm)

The 30 or so species in this genus of trees occur naturally in temperate regions of the northern hemisphere. During the 1920's and 1930's, and again in the 1960's and 1970's, elm trees in Europe and North America were devastated by Dutch elm disease, caused by the fungus Ophiostoma ulmi, which is transmitted by the elm bark beetle. Except for a few East Asian species, they are deciduous, turning yellow in fall. The leaves are usually one-sided at the base, with prominent, parallel lateral veins and regularly toothed margins; the small, disc-like fruits have membranous wing and are carried in cluster. Most elms are large limbed with furrowed gray bark and high, domed crowns.

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