For alternatives to these exotic or problem shade trees: Siberian elm (Ulmus pumila) Tree of heaven (Ailanthus altissima) Norway maple (Acer platanoides) As well as: Ash (Fraxinus spp.) – for the emerald ash borer threat We recommend the following site for control of Siberian elm and other exotic or problem trees: Illinois Weed Management Guides (Click on Siberian elm and other trees.)
Forma inermis is a thornless variety of G. triacanthos that occurs naturally in the wild. It grows to the same height as the thorny species (60-80’). Cultivars of G. triacanthos which are sold in commerce today are all from f. inermis (no thorns and in many cases no seedpods, which makes them preferred landscape plants). Pinnate to bipinnate dark green leaves with small leaflets cast a sun-dappled shade. Leaves turn an attractive yellow in fall.
More Selections
For additional selections including cultivars and non-native shade trees we recommend "Alternatives to Ash" by Jeff Iles, Department of Horticulture, Iowa State University.