The hybrid cultivar 'Willis' originated as a selection made by a Mr Minnick of Kansas

Kansas

Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

 simply as a hybrid. Almost certainly derived from a crossing of the Siberian Elm

Siberian Elm

Ulmus pumila, the Siberian Elm, is native to Central Asia, eastern Siberia, Mongolia, Xizang , northern China, India and Korea . It is also known as the Asiatic Elm, Dwarf Elm and Chinese Elm. Two varieties are recognized: var pumila and var. arborea, the latter known as Turkestan elm...

 Ulmus pumila and the Red Elm Ulmus rubra

Ulmus rubra

Ulmus rubra, the Slippery Elm, is a species of elm native to eastern North America...

, it was originally believed that the American parent was the American Elm

American Elm

Ulmus americana, generally known as the American Elm or, less commonly, as the White Elm or Water Elm, is a species native to eastern North America, occurring from Nova Scotia west to Alberta and Montana, and south to Florida and central Texas. The American elm is an extremely hardy tree that can...

 Ulmus americana, not the Red Elm.

Description

'Willis' was described as having a smooth grey bark, large leaves similar to U. americana, and capable of very rapid growth .

Cultivation

First marketed by the Willis Nursery Co., Ottawa

Ottawa, Kansas

Ottawa is a city situated along the Marais des Cygnes River in the central part of Franklin County, located in east-central Kansas, 50 miles southwest of Kansas City, Mo., in the central United States. As of the 2010 census, the city population was 12,649. It is the county seat and most populous...

, Kansas

Kansas

Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

, circa 1959, it is not known whether the cultivar remains in cultivation in the USA, nor whether it was ever introduced to Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

 or Australasia

Australasia

Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...

.