Distribution: Worldwide across northern, temperate regions. 3 genera (Elm - Ulmus, Hackberry - Celtis, and Water Elm - Planera) with 12 species in the Texas flora. The Elm lineage, like many genera of the Hamamelidae, includes both European and American species of Ulmus with each continental group of species evolving in isolation for many generations. While European taxa evolved in the presence of the fungus Ophiostoma novo-ulmi, and natural selection in Europe resulted in some resistance, this fungus was not present in North America and resistance was not part of the American Elm (Ulmus americana) genome. Thus, when the fungus was carried to North America in the 1930s it quickly took advantage of the American Elm, then a dominant species of our forests and often cultivated along streets. The resulting population crash for this species might be reversed by human selection for resistance among surviving plants.
Unusual, within the context of the Subclass, by the presence of
in the perianth and, in some genera - such as Ulmus -
flowers. All elements of the family tend to show leaf asymmetry,
or oblique leaf blade bases, and
is a good recognition character.
|Oblique leaf base in two
||Celtis - imperfect flowers - monoecious (from the University of Hawaii)||Ulmus - perfect flowers|
Like many elements of the Hamamelidae, the Ulmaceae is not a large element of the flowering plant lineage in terms of species diversity BUT individual species of the family are important components of the world's deciduous forests and, in our flora, the Winged Elm (U. alata - dist) is common in the Post Oak uplands with both the Cedar Elm (U. crassifolia - dist) and Hackberry (or 'Texas Sugarberry') - Celtis laevigata - dist major components of floodplain forests.
More information on the Ulmaceae