| Ulmus × intermedia cultivar | |
| Hybrid: | U. pumila × U. rubra |
| Cultivar: | 'Willis' |
| Origin: | US |
The hybrid elm cultivar Ulmus × intermedia 'Willis' originated as a crossing made by a Mr Minnick of Kansas. Almost certainly derived from a crossing of the Siberian Elm Ulmus pumila (female parent) and the Red Elm Ulmus rubra, it was originally believed that the male parent was the American Elm Ulmus americana.[1]
'Willis' was described as having a smooth grey bark, large leaves similar to U. americana, and capable of very rapid growth.[1]
In 1995 Santamour reported the cultivar "not widely tested for resistance to Dutch elm disease".[2] Elowsky, Jordon-Thaden, and Kaul (2013) refer to more recent papers on the subject.[3]
First marketed by the Willis Nursery Co., Ottawa, Kansas, circa 1959,[2] it is not known whether the cultivar remains in cultivation in the United States, nor whether it was ever introduced to Europe or Australasia.