Tree Indiana Native Ulmus rubra [Slippery Elm] The Slippery Elm has a vase-shaped form, similar to that of the American Elm (Ulmus americana), but with more ascending branchlets. This tree gained its common name from the moist, slippery, red inner bark chewed by Native Americans and pioneers to quench thirst. Not considered very ornamental for the landscape, due to its coarse texture, weedy tendencies, and susceptibility to Dutch Elm Disease (although not as severe as the American Elm).