The Hamamelidae
Family Overview - The Urticales
Ulmaceae - the Elm Family

Diversity:  A family of 18 genera and about 150 species of woody plants, mostly trees.

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.

Floral structure:

Significant features:  Unusual, within the context of the Subclass, by the presence of connation in the perianth and, in some genera - such as Ulmus - perfect flowers.  All elements of the family tend to show leaf asymmetry, or oblique leaf blade bases, and this is a good recognition character.

Oblique leaf base in two genera
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

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11 Feb 2011